what is abstract in literature review

How to Write a Literature Review

• Critical analysis
• Sample Literature Reviews
• Scaffold examples for organising Literature Reviews
• Writing an Abstract
• Creating Appendices
• APA Reference Guide
• Library Resources
• Guide References

What is an abstract?

What is an Abstract?

An abstract is a short summary of an article, essay or research findings. A well-written abstract will provide the reader with a brief overview of the entire article, including the article's purpose, methodology and conclusion. An abstract should give the reader enough detail to determine if the information in the article meets their research needs...and it should make them want to read more!

While an abstract is usually anywhere between 150 - 300 words, it is important to always establish with your teacher the desired length of the abstract you are submitting.

This excellent guide from the University of Melbourne is a great snapshot of how to write an abstract.

Here are a few links to some useful abstract examples:

University of New South Wales

University of Wollongong

Michigan State University

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How do I Write a Literature Review?: #5 Writing the Review

• Step #1: Choosing a Topic
• Step #2: Finding Information
• Step #3: Evaluating Content
• Step #4: Synthesizing Content
• #5 Writing the Review
• Citing Your Sources

WRITING THE REVIEW 

You've done the research and now you're ready to put your findings down on paper. When preparing to write your review, first consider how will you organize your review.

The actual review generally has 5 components:

Abstract  -  An abstract is a summary of your literature review. It is made up of the following parts:

• A contextual sentence about your motivation behind your research topic
• Your thesis statement
• A descriptive statement about the types of literature used in the review
• Summarize your findings
• Conclusion(s) based upon your findings

Introduction :   Like a typical research paper introduction, provide the reader with a quick idea of the topic of the literature review:

• Define or identify the general topic, issue, or area of concern. This provides the reader with context for reviewing the literature.
• Identify related trends in what has already been published about the topic; or conflicts in theory, methodology, evidence, and conclusions; or gaps in research and scholarship; or a single problem or new perspective of immediate interest.
• Establish your reason (point of view) for reviewing the literature; explain the criteria to be used in analyzing and comparing literature and the organization of the review (sequence); and, when necessary, state why certain literature is or is not included (scope)  - 

Body :  The body of a literature review contains your discussion of sources and can be organized in 3 ways-

• Chronological -  by publication or by trend
• Thematic -  organized around a topic or issue, rather than the progression of time
• Methodical -  the focusing factor usually does not have to do with the content of the material. Instead, it focuses on the "methods" of the literature's researcher or writer that you are reviewing

You may also want to include a section on "questions for further research" and discuss what questions the review has sparked about the topic/field or offer suggestions for future studies/examinations that build on your current findings.

Conclusion :  In the conclusion, you should:

Conclude your paper by providing your reader with some perspective on the relationship between your literature review's specific topic and how it's related to it's parent discipline, scientific endeavor, or profession.

Bibliography :   Since a literature review is composed of pieces of research, it is very important that your correctly cite the literature you are reviewing, both in the reviews body as well as in a bibliography/works cited. To learn more about different citation styles, visit the " Citing Your Sources " tab.

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Writing an Abstract for Your Research Paper

Definition and Purpose of Abstracts

An abstract is a short summary of your (published or unpublished) research paper, usually about a paragraph (c. 6-7 sentences, 150-250 words) long. A well-written abstract serves multiple purposes:

• an abstract lets readers get the gist or essence of your paper or article quickly, in order to decide whether to read the full paper;
• an abstract prepares readers to follow the detailed information, analyses, and arguments in your full paper;
• and, later, an abstract helps readers remember key points from your paper.

It’s also worth remembering that search engines and bibliographic databases use abstracts, as well as the title, to identify key terms for indexing your published paper. So what you include in your abstract and in your title are crucial for helping other researchers find your paper or article.

If you are writing an abstract for a course paper, your professor may give you specific guidelines for what to include and how to organize your abstract. Similarly, academic journals often have specific requirements for abstracts. So in addition to following the advice on this page, you should be sure to look for and follow any guidelines from the course or journal you’re writing for.

The Contents of an Abstract

Abstracts contain most of the following kinds of information in brief form. The body of your paper will, of course, develop and explain these ideas much more fully. As you will see in the samples below, the proportion of your abstract that you devote to each kind of information—and the sequence of that information—will vary, depending on the nature and genre of the paper that you are summarizing in your abstract. And in some cases, some of this information is implied, rather than stated explicitly. The Publication Manual of the American Psychological Association , which is widely used in the social sciences, gives specific guidelines for what to include in the abstract for different kinds of papers—for empirical studies, literature reviews or meta-analyses, theoretical papers, methodological papers, and case studies.

Here are the typical kinds of information found in most abstracts:

• the context or background information for your research; the general topic under study; the specific topic of your research
• the central questions or statement of the problem your research addresses
• what’s already known about this question, what previous research has done or shown
• the main reason(s) , the exigency, the rationale , the goals for your research—Why is it important to address these questions? Are you, for example, examining a new topic? Why is that topic worth examining? Are you filling a gap in previous research? Applying new methods to take a fresh look at existing ideas or data? Resolving a dispute within the literature in your field? . . .
• your research and/or analytical methods
• your main findings , results , or arguments
• the significance or implications of your findings or arguments.

Your abstract should be intelligible on its own, without a reader’s having to read your entire paper. And in an abstract, you usually do not cite references—most of your abstract will describe what you have studied in your research and what you have found and what you argue in your paper. In the body of your paper, you will cite the specific literature that informs your research.

When to Write Your Abstract

Although you might be tempted to write your abstract first because it will appear as the very first part of your paper, it’s a good idea to wait to write your abstract until after you’ve drafted your full paper, so that you know what you’re summarizing.

What follows are some sample abstracts in published papers or articles, all written by faculty at UW-Madison who come from a variety of disciplines. We have annotated these samples to help you see the work that these authors are doing within their abstracts.

Choosing Verb Tenses within Your Abstract

The social science sample (Sample 1) below uses the present tense to describe general facts and interpretations that have been and are currently true, including the prevailing explanation for the social phenomenon under study. That abstract also uses the present tense to describe the methods, the findings, the arguments, and the implications of the findings from their new research study. The authors use the past tense to describe previous research.

The humanities sample (Sample 2) below uses the past tense to describe completed events in the past (the texts created in the pulp fiction industry in the 1970s and 80s) and uses the present tense to describe what is happening in those texts, to explain the significance or meaning of those texts, and to describe the arguments presented in the article.

The science samples (Samples 3 and 4) below use the past tense to describe what previous research studies have done and the research the authors have conducted, the methods they have followed, and what they have found. In their rationale or justification for their research (what remains to be done), they use the present tense. They also use the present tense to introduce their study (in Sample 3, “Here we report . . .”) and to explain the significance of their study (In Sample 3, This reprogramming . . . “provides a scalable cell source for. . .”).

Sample Abstract 1

From the social sciences.

Reporting new findings about the reasons for increasing economic homogamy among spouses

Gonalons-Pons, Pilar, and Christine R. Schwartz. “Trends in Economic Homogamy: Changes in Assortative Mating or the Division of Labor in Marriage?” Demography , vol. 54, no. 3, 2017, pp. 985-1005.

Sample Abstract 2

From the humanities.

Analyzing underground pulp fiction publications in Tanzania, this article makes an argument about the cultural significance of those publications

Emily Callaci. “Street Textuality: Socialism, Masculinity, and Urban Belonging in Tanzania’s Pulp Fiction Publishing Industry, 1975-1985.” Comparative Studies in Society and History , vol. 59, no. 1, 2017, pp. 183-210.

Sample Abstract/Summary 3

From the sciences.

Reporting a new method for reprogramming adult mouse fibroblasts into induced cardiac progenitor cells

Lalit, Pratik A., Max R. Salick, Daryl O. Nelson, Jayne M. Squirrell, Christina M. Shafer, Neel G. Patel, Imaan Saeed, Eric G. Schmuck, Yogananda S. Markandeya, Rachel Wong, Martin R. Lea, Kevin W. Eliceiri, Timothy A. Hacker, Wendy C. Crone, Michael Kyba, Daniel J. Garry, Ron Stewart, James A. Thomson, Karen M. Downs, Gary E. Lyons, and Timothy J. Kamp. “Lineage Reprogramming of Fibroblasts into Proliferative Induced Cardiac Progenitor Cells by Defined Factors.” Cell Stem Cell , vol. 18, 2016, pp. 354-367.

Sample Abstract 4, a Structured Abstract

Reporting results about the effectiveness of antibiotic therapy in managing acute bacterial sinusitis, from a rigorously controlled study

Note: This journal requires authors to organize their abstract into four specific sections, with strict word limits. Because the headings for this structured abstract are self-explanatory, we have chosen not to add annotations to this sample abstract.

Wald, Ellen R., David Nash, and Jens Eickhoff. “Effectiveness of Amoxicillin/Clavulanate Potassium in the Treatment of Acute Bacterial Sinusitis in Children.” Pediatrics , vol. 124, no. 1, 2009, pp. 9-15.

“OBJECTIVE: The role of antibiotic therapy in managing acute bacterial sinusitis (ABS) in children is controversial. The purpose of this study was to determine the effectiveness of high-dose amoxicillin/potassium clavulanate in the treatment of children diagnosed with ABS.

METHODS : This was a randomized, double-blind, placebo-controlled study. Children 1 to 10 years of age with a clinical presentation compatible with ABS were eligible for participation. Patients were stratified according to age (<6 or ≥6 years) and clinical severity and randomly assigned to receive either amoxicillin (90 mg/kg) with potassium clavulanate (6.4 mg/kg) or placebo. A symptom survey was performed on days 0, 1, 2, 3, 5, 7, 10, 20, and 30. Patients were examined on day 14. Children’s conditions were rated as cured, improved, or failed according to scoring rules.

RESULTS: Two thousand one hundred thirty-five children with respiratory complaints were screened for enrollment; 139 (6.5%) had ABS. Fifty-eight patients were enrolled, and 56 were randomly assigned. The mean age was 6630 months. Fifty (89%) patients presented with persistent symptoms, and 6 (11%) presented with nonpersistent symptoms. In 24 (43%) children, the illness was classified as mild, whereas in the remaining 32 (57%) children it was severe. Of the 28 children who received the antibiotic, 14 (50%) were cured, 4 (14%) were improved, 4(14%) experienced treatment failure, and 6 (21%) withdrew. Of the 28children who received placebo, 4 (14%) were cured, 5 (18%) improved, and 19 (68%) experienced treatment failure. Children receiving the antibiotic were more likely to be cured (50% vs 14%) and less likely to have treatment failure (14% vs 68%) than children receiving the placebo.

CONCLUSIONS : ABS is a common complication of viral upper respiratory infections. Amoxicillin/potassium clavulanate results in significantly more cures and fewer failures than placebo, according to parental report of time to resolution.” (9)

Some Excellent Advice about Writing Abstracts for Basic Science Research Papers, by Professor Adriano Aguzzi from the Institute of Neuropathology at the University of Zurich:

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What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

Prevent plagiarism, run a free check.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

Cite this Scribbr article

If you want to cite this source, you can copy and paste the citation or click the ‘Cite this Scribbr article’ button to automatically add the citation to our free Reference Generator.

McCombes, S. (2022, June 07). What is a Literature Review? | Guide, Template, & Examples. Scribbr. Retrieved 22 April 2024, from https://www.scribbr.co.uk/thesis-dissertation/literature-review/

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

What this handout is about

This handout provides definitions and examples of the two main types of abstracts: descriptive and informative. It also provides guidelines for constructing an abstract and general tips for you to keep in mind when drafting. Finally, it includes a few examples of abstracts broken down into their component parts.

What is an abstract?

An abstract is a self-contained, short, and powerful statement that describes a larger work. Components vary according to discipline. An abstract of a social science or scientific work may contain the scope, purpose, results, and contents of the work. An abstract of a humanities work may contain the thesis, background, and conclusion of the larger work. An abstract is not a review, nor does it evaluate the work being abstracted. While it contains key words found in the larger work, the abstract is an original document rather than an excerpted passage.

Why write an abstract?

You may write an abstract for various reasons. The two most important are selection and indexing. Abstracts allow readers who may be interested in a longer work to quickly decide whether it is worth their time to read it. Also, many online databases use abstracts to index larger works. Therefore, abstracts should contain keywords and phrases that allow for easy searching.

Say you are beginning a research project on how Brazilian newspapers helped Brazil’s ultra-liberal president Luiz Ignácio da Silva wrest power from the traditional, conservative power base. A good first place to start your research is to search Dissertation Abstracts International for all dissertations that deal with the interaction between newspapers and politics. “Newspapers and politics” returned 569 hits. A more selective search of “newspapers and Brazil” returned 22 hits. That is still a fair number of dissertations. Titles can sometimes help winnow the field, but many titles are not very descriptive. For example, one dissertation is titled “Rhetoric and Riot in Rio de Janeiro.” It is unclear from the title what this dissertation has to do with newspapers in Brazil. One option would be to download or order the entire dissertation on the chance that it might speak specifically to the topic. A better option is to read the abstract. In this case, the abstract reveals the main focus of the dissertation:

This dissertation examines the role of newspaper editors in the political turmoil and strife that characterized late First Empire Rio de Janeiro (1827-1831). Newspaper editors and their journals helped change the political culture of late First Empire Rio de Janeiro by involving the people in the discussion of state. This change in political culture is apparent in Emperor Pedro I’s gradual loss of control over the mechanisms of power. As the newspapers became more numerous and powerful, the Emperor lost his legitimacy in the eyes of the people. To explore the role of the newspapers in the political events of the late First Empire, this dissertation analyzes all available newspapers published in Rio de Janeiro from 1827 to 1831. Newspapers and their editors were leading forces in the effort to remove power from the hands of the ruling elite and place it under the control of the people. In the process, newspapers helped change how politics operated in the constitutional monarchy of Brazil.

From this abstract you now know that although the dissertation has nothing to do with modern Brazilian politics, it does cover the role of newspapers in changing traditional mechanisms of power. After reading the abstract, you can make an informed judgment about whether the dissertation would be worthwhile to read.

Besides selection, the other main purpose of the abstract is for indexing. Most article databases in the online catalog of the library enable you to search abstracts. This allows for quick retrieval by users and limits the extraneous items recalled by a “full-text” search. However, for an abstract to be useful in an online retrieval system, it must incorporate the key terms that a potential researcher would use to search. For example, if you search Dissertation Abstracts International using the keywords “France” “revolution” and “politics,” the search engine would search through all the abstracts in the database that included those three words. Without an abstract, the search engine would be forced to search titles, which, as we have seen, may not be fruitful, or else search the full text. It’s likely that a lot more than 60 dissertations have been written with those three words somewhere in the body of the entire work. By incorporating keywords into the abstract, the author emphasizes the central topics of the work and gives prospective readers enough information to make an informed judgment about the applicability of the work.

When do people write abstracts?

• when submitting articles to journals, especially online journals
• when applying for research grants
• when writing a book proposal
• when completing the Ph.D. dissertation or M.A. thesis
• when writing a proposal for a conference paper
• when writing a proposal for a book chapter

Most often, the author of the entire work (or prospective work) writes the abstract. However, there are professional abstracting services that hire writers to draft abstracts of other people’s work. In a work with multiple authors, the first author usually writes the abstract. Undergraduates are sometimes asked to draft abstracts of books/articles for classmates who have not read the larger work.

Types of abstracts

There are two types of abstracts: descriptive and informative. They have different aims, so as a consequence they have different components and styles. There is also a third type called critical, but it is rarely used. If you want to find out more about writing a critique or a review of a work, see the UNC Writing Center handout on writing a literature review . If you are unsure which type of abstract you should write, ask your instructor (if the abstract is for a class) or read other abstracts in your field or in the journal where you are submitting your article.

Descriptive abstracts

A descriptive abstract indicates the type of information found in the work. It makes no judgments about the work, nor does it provide results or conclusions of the research. It does incorporate key words found in the text and may include the purpose, methods, and scope of the research. Essentially, the descriptive abstract describes the work being abstracted. Some people consider it an outline of the work, rather than a summary. Descriptive abstracts are usually very short—100 words or less.

Informative abstracts

The majority of abstracts are informative. While they still do not critique or evaluate a work, they do more than describe it. A good informative abstract acts as a surrogate for the work itself. That is, the writer presents and explains all the main arguments and the important results and evidence in the complete article/paper/book. An informative abstract includes the information that can be found in a descriptive abstract (purpose, methods, scope) but also includes the results and conclusions of the research and the recommendations of the author. The length varies according to discipline, but an informative abstract is rarely more than 10% of the length of the entire work. In the case of a longer work, it may be much less.

Here are examples of a descriptive and an informative abstract of this handout on abstracts . Descriptive abstract:

The two most common abstract types—descriptive and informative—are described and examples of each are provided.

Informative abstract:

Abstracts present the essential elements of a longer work in a short and powerful statement. The purpose of an abstract is to provide prospective readers the opportunity to judge the relevance of the longer work to their projects. Abstracts also include the key terms found in the longer work and the purpose and methods of the research. Authors abstract various longer works, including book proposals, dissertations, and online journal articles. There are two main types of abstracts: descriptive and informative. A descriptive abstract briefly describes the longer work, while an informative abstract presents all the main arguments and important results. This handout provides examples of various types of abstracts and instructions on how to construct one.

Which type should I use?

Your best bet in this case is to ask your instructor or refer to the instructions provided by the publisher. You can also make a guess based on the length allowed; i.e., 100-120 words = descriptive; 250+ words = informative.

How do I write an abstract?

The format of your abstract will depend on the work being abstracted. An abstract of a scientific research paper will contain elements not found in an abstract of a literature article, and vice versa. However, all abstracts share several mandatory components, and there are also some optional parts that you can decide to include or not. When preparing to draft your abstract, keep the following key process elements in mind:

• Reason for writing: What is the importance of the research? Why would a reader be interested in the larger work?
• Problem: What problem does this work attempt to solve? What is the scope of the project? What is the main argument/thesis/claim?
• Methodology: An abstract of a scientific work may include specific models or approaches used in the larger study. Other abstracts may describe the types of evidence used in the research.
• Results: Again, an abstract of a scientific work may include specific data that indicates the results of the project. Other abstracts may discuss the findings in a more general way.
• Implications: What changes should be implemented as a result of the findings of the work? How does this work add to the body of knowledge on the topic?

(This list of elements is adapted with permission from Philip Koopman, “How to Write an Abstract.” )

All abstracts include:

• A full citation of the source, preceding the abstract.
• The most important information first.
• The same type and style of language found in the original, including technical language.
• Key words and phrases that quickly identify the content and focus of the work.
• Clear, concise, and powerful language.

Abstracts may include:

• The thesis of the work, usually in the first sentence.
• Background information that places the work in the larger body of literature.
• The same chronological structure as the original work.

How not to write an abstract:

• Do not refer extensively to other works.
• Do not add information not contained in the original work.
• Do not define terms.

If you are abstracting your own writing

When abstracting your own work, it may be difficult to condense a piece of writing that you have agonized over for weeks (or months, or even years) into a 250-word statement. There are some tricks that you could use to make it easier, however.

Reverse outlining:

This technique is commonly used when you are having trouble organizing your own writing. The process involves writing down the main idea of each paragraph on a separate piece of paper– see our short video . For the purposes of writing an abstract, try grouping the main ideas of each section of the paper into a single sentence. Practice grouping ideas using webbing or color coding .

For a scientific paper, you may have sections titled Purpose, Methods, Results, and Discussion. Each one of these sections will be longer than one paragraph, but each is grouped around a central idea. Use reverse outlining to discover the central idea in each section and then distill these ideas into one statement.

Cut and paste:

To create a first draft of an abstract of your own work, you can read through the entire paper and cut and paste sentences that capture key passages. This technique is useful for social science research with findings that cannot be encapsulated by neat numbers or concrete results. A well-written humanities draft will have a clear and direct thesis statement and informative topic sentences for paragraphs or sections. Isolate these sentences in a separate document and work on revising them into a unified paragraph.

If you are abstracting someone else’s writing

When abstracting something you have not written, you cannot summarize key ideas just by cutting and pasting. Instead, you must determine what a prospective reader would want to know about the work. There are a few techniques that will help you in this process:

Identify key terms:

Search through the entire document for key terms that identify the purpose, scope, and methods of the work. Pay close attention to the Introduction (or Purpose) and the Conclusion (or Discussion). These sections should contain all the main ideas and key terms in the paper. When writing the abstract, be sure to incorporate the key terms.

Highlight key phrases and sentences:

Instead of cutting and pasting the actual words, try highlighting sentences or phrases that appear to be central to the work. Then, in a separate document, rewrite the sentences and phrases in your own words.

Don’t look back:

After reading the entire work, put it aside and write a paragraph about the work without referring to it. In the first draft, you may not remember all the key terms or the results, but you will remember what the main point of the work was. Remember not to include any information you did not get from the work being abstracted.

Revise, revise, revise

No matter what type of abstract you are writing, or whether you are abstracting your own work or someone else’s, the most important step in writing an abstract is to revise early and often. When revising, delete all extraneous words and incorporate meaningful and powerful words. The idea is to be as clear and complete as possible in the shortest possible amount of space. The Word Count feature of Microsoft Word can help you keep track of how long your abstract is and help you hit your target length.

Example 1: Humanities abstract

Kenneth Tait Andrews, “‘Freedom is a constant struggle’: The dynamics and consequences of the Mississippi Civil Rights Movement, 1960-1984” Ph.D. State University of New York at Stony Brook, 1997 DAI-A 59/02, p. 620, Aug 1998

This dissertation examines the impacts of social movements through a multi-layered study of the Mississippi Civil Rights Movement from its peak in the early 1960s through the early 1980s. By examining this historically important case, I clarify the process by which movements transform social structures and the constraints movements face when they try to do so. The time period studied includes the expansion of voting rights and gains in black political power, the desegregation of public schools and the emergence of white-flight academies, and the rise and fall of federal anti-poverty programs. I use two major research strategies: (1) a quantitative analysis of county-level data and (2) three case studies. Data have been collected from archives, interviews, newspapers, and published reports. This dissertation challenges the argument that movements are inconsequential. Some view federal agencies, courts, political parties, or economic elites as the agents driving institutional change, but typically these groups acted in response to the leverage brought to bear by the civil rights movement. The Mississippi movement attempted to forge independent structures for sustaining challenges to local inequities and injustices. By propelling change in an array of local institutions, movement infrastructures had an enduring legacy in Mississippi.

Now let’s break down this abstract into its component parts to see how the author has distilled his entire dissertation into a ~200 word abstract.

What the dissertation does This dissertation examines the impacts of social movements through a multi-layered study of the Mississippi Civil Rights Movement from its peak in the early 1960s through the early 1980s. By examining this historically important case, I clarify the process by which movements transform social structures and the constraints movements face when they try to do so.

How the dissertation does it The time period studied in this dissertation includes the expansion of voting rights and gains in black political power, the desegregation of public schools and the emergence of white-flight academies, and the rise and fall of federal anti-poverty programs. I use two major research strategies: (1) a quantitative analysis of county-level data and (2) three case studies.

What materials are used Data have been collected from archives, interviews, newspapers, and published reports.

Conclusion This dissertation challenges the argument that movements are inconsequential. Some view federal agencies, courts, political parties, or economic elites as the agents driving institutional change, but typically these groups acted in response to movement demands and the leverage brought to bear by the civil rights movement. The Mississippi movement attempted to forge independent structures for sustaining challenges to local inequities and injustices. By propelling change in an array of local institutions, movement infrastructures had an enduring legacy in Mississippi.

Keywords social movements Civil Rights Movement Mississippi voting rights desegregation

Example 2: Science Abstract

Luis Lehner, “Gravitational radiation from black hole spacetimes” Ph.D. University of Pittsburgh, 1998 DAI-B 59/06, p. 2797, Dec 1998

The problem of detecting gravitational radiation is receiving considerable attention with the construction of new detectors in the United States, Europe, and Japan. The theoretical modeling of the wave forms that would be produced in particular systems will expedite the search for and analysis of detected signals. The characteristic formulation of GR is implemented to obtain an algorithm capable of evolving black holes in 3D asymptotically flat spacetimes. Using compactification techniques, future null infinity is included in the evolved region, which enables the unambiguous calculation of the radiation produced by some compact source. A module to calculate the waveforms is constructed and included in the evolution algorithm. This code is shown to be second-order convergent and to handle highly non-linear spacetimes. In particular, we have shown that the code can handle spacetimes whose radiation is equivalent to a galaxy converting its whole mass into gravitational radiation in one second. We further use the characteristic formulation to treat the region close to the singularity in black hole spacetimes. The code carefully excises a region surrounding the singularity and accurately evolves generic black hole spacetimes with apparently unlimited stability.

This science abstract covers much of the same ground as the humanities one, but it asks slightly different questions.

Why do this study The problem of detecting gravitational radiation is receiving considerable attention with the construction of new detectors in the United States, Europe, and Japan. The theoretical modeling of the wave forms that would be produced in particular systems will expedite the search and analysis of the detected signals.

What the study does The characteristic formulation of GR is implemented to obtain an algorithm capable of evolving black holes in 3D asymptotically flat spacetimes. Using compactification techniques, future null infinity is included in the evolved region, which enables the unambiguous calculation of the radiation produced by some compact source. A module to calculate the waveforms is constructed and included in the evolution algorithm.

Results This code is shown to be second-order convergent and to handle highly non-linear spacetimes. In particular, we have shown that the code can handle spacetimes whose radiation is equivalent to a galaxy converting its whole mass into gravitational radiation in one second. We further use the characteristic formulation to treat the region close to the singularity in black hole spacetimes. The code carefully excises a region surrounding the singularity and accurately evolves generic black hole spacetimes with apparently unlimited stability.

Keywords gravitational radiation (GR) spacetimes black holes

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Belcher, Wendy Laura. 2009. Writing Your Journal Article in Twelve Weeks: A Guide to Academic Publishing Success. Thousand Oaks, CA: Sage Press.

Koopman, Philip. 1997. “How to Write an Abstract.” Carnegie Mellon University. October 1997. http://users.ece.cmu.edu/~koopman/essays/abstract.html .

Lancaster, F.W. 2003. Indexing And Abstracting in Theory and Practice , 3rd ed. London: Facet Publishing.

You may reproduce it for non-commercial use if you use the entire handout and attribute the source: The Writing Center, University of North Carolina at Chapel Hill

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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 
• How to write a good literature review 
• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

• Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 
• Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 
• Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 
• Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 
• Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 
• Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

How to write a good literature review

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. 

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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Write Abstracts, Literature Reviews, and Annotated Bibliographies: Abstract Guides & Examples

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What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

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Clarifying the abstracts of systematic literature reviews *

James hartley.

1 Department of Psychology Keele University Staffordshire United Kingdom

2 † Author's address for correspondence: James Hartley, B.A., Ph.D., Department of Psychology, Keele University, Staffordshire, ST5 5BG, United Kingdom; email, [email protected]

Background: There is a small body of research on improving the clarity of abstracts in general that is relevant to improving the clarity of abstracts of systematic reviews.

Objectives: To summarize this earlier research and indicate its implications for writing the abstracts of systematic reviews.

Method: Literature review with commentary on three main features affecting the clarity of abstracts: their language, structure, and typographical presentation.

Conclusions: The abstracts of systematic reviews should be easier to read than the abstracts of medical research articles, as they are targeted at a wider audience. The aims, methods, results, and conclusions of systematic reviews need to be presented in a consistent way to help search and retrieval. The typographic detailing of the abstracts (type-sizes, spacing, and weights) should be planned to help, rather than confuse, the reader.

Several books and review papers have been published over the last twenty-five years about improving the clarity of the abstracts of articles in scientific journals, including several recent studies [ 1–5 ]. Three main areas of importance have been discussed:

• the language, or the readability, of an abstract;
• the sequence of information, or the structure, of an abstract; and
• the typography, or the presentation, of an abstract.

This paper considers the implications of the findings from research in each of these overlapping areas to the more specific area of writing abstracts for what are called “systematic reviews.” Such reviews in medical journals typically use standard procedures for assessing the evidence obtained from separate studies for and against the effectiveness of a particular treatment. The term “systematic” implies that the authors have used a standard approach to minimizing biases and random errors and that the methods chosen for the approach will be documented in the materials and methods sections of the review. Examples of such reviews may be found in Chalmers's and Altman's text [ 6 ] and in papers published in medical journals, particularly Evidence-Based Medicine. Figure 1 provides a fictitious example of an abstract for such a paper.

“Before” and “after” examples designed to show how differences in typography and wording can enhance the clarity of an abstract. Abstract courtesy of Philippa Middleton.

THE LANGUAGE OF THE TEXT

Research on the readability of conventional journal abstracts suggests that they are not easy to read. Studies in this area typically use the Flesch Reading Ease (R.E.) scores as their measure of text difficulty [ 7 ]. This measure, developed in the 1940s, is based upon the somewhat over simple idea that the difficulty of text is a function of the length of the sentences in the text and the length of the words within these sentences. The original Flesch formula is that R.E. = 206.835 − 0.846w − 1.015s (where w = the average number of syllables in 100 words and s = the average number of words per sentence). The scores normally range from 0 to 100, and the lower the score the more difficult the text is to read; Table 1 gives typical examples. Today, Flesch R.E. scores accompany most computerized spell checkers, and this removes the difficulties of hand calculation; although different programs give slightly different results [ 8, 9 ].

Table 1 The interpretation of Flesch scores

Table 2 summarizes the Flesch scores obtained for numerous journal abstracts in seven studies. The low scores shown here support the notion that journal abstracts are difficult to read. With medical journals, in particular, this difficulty may stem partly from complex medical terminology. Readability scores such as these are widely quoted, even though there is considerable debate about their validity, largely because they ignore the readers' prior knowledge and motivation [ 10, 11 ].

Table 2 Flesch Reading Ease scores reported in previous research on abstracts in journal articles

A second cause of difficulty in understanding text is that, although the wording may be simple and the sentences short, the concepts being described may not be understood by the reader. Thus, for example, although the sentence “God is grace” is extremely readable (in terms of the Flesch), it is not easy to explain what it actually means! In systematic reviews, to be more specific, the statistical concepts of the confidence interval and the adjusted odds ratio ( Figure 1 ) may be well understood by medical researchers, but they will not be understood by all readers.

A third cause of difficulty in prose lies in the scientific nature of the text that emphasizes the use of the third person, together with the passive rather than the active tense. Graetz writes of journal abstracts:

The abstract is characterized by the use of the past tense, the third person, passive, and the non-use of negatives…. It is written in tightly worded sentences, which avoid repetition, meaningless expressions, superlatives, adjectives, illustrations, preliminaries, descriptive details, examples, footnotes. In short it eliminates the redundancy which the skilled reader counts on finding in written language and which usually facilitates comprehension. [ 12 ]

In systematic reviews, it is easy to find sentences like “Trial eligibility and quality were assessed” that would be more readable if they were written as “We assessed the eligibility and the quality of the trials.” Furthermore, there are often short telegrammatic communications, some of which contain no verbs. Figure 1 provides an example (under the subheading “Selection criteria”).

There are, of course, numerous guidelines on how to write clear abstracts and more readable medical text [ 13–16 ] but, at present, there are few such guidelines for writing the abstracts of systematic reviews. Mulrow, Thacker, and Pugh [ 17 ] provide an excellent early example, and there are now regularly updated guidelines in the Cochrane Handbook [ 18 ].

Nonetheless, even when such guidelines are followed, evaluating the clarity of medical text is not easy. But some methods of doing so may be adapted from the more traditional literature on text evaluation. Schriver, for example, describes three different methods of text evaluation—text-based, expert-based, and reader-based methods [ 19 ]:

• Text-based methods are ones that can be used without recourse to experts or to readers. Such methods include computer-based readability formulae (such as the Flesch measure described above) and computer-based measures of style and grammar.
• Expert-based methods are ones that use experts to make assessments of the effectiveness of a piece of text. Medical experts may be asked, for example, to judge the suitability of the information contained in a patient information leaflet.
• Reader-based methods are ones that involve actual readers in making assessments of the suitability of the text, for themselves and for others. Patients, for example, may be asked to comment on medical leaflets or be tested on how much they can recall from them.

Although all three methods of evaluation are useful, especially in combination, this writer particularly recommends reader-based methods for evaluating the readability of abstracts in systematic reviews. This recommendation is because the readers of such systematic reviews are likely to be quite disparate in their aims, needs, and even in the languages that they speak. As the 1999 Cochrane Handbook put it:

Abstracts should be made as readable as possible without compromising scientific integrity. They should primarily be targeted to health care decision makers (clinicians, consumers, and policy makers) rather than just researchers. Terminology should be reasonably comprehensible to a general rather than a specialist medical audience [emphasis added]. [ 20 ]

Expert-based measures on their own may be misleading. For instance, there is evidence to suggest that the concerns of professionals are different from those of other personnel [ 21 ]. Wilson et al. [ 22 ], for instance, report wide differences between the responses of general practitioners (GPs) and patients in the United Kingdom in responses to questions concerning the content and usefulness of several patient information leaflets. Table 3 shows some of their replies.

Table 3 Differences between general practitioners (GPs) and patients in their views about particular patient information leaflets

THE STRUCTURE OF THE TEXT

In recent times, particularly in the medical field, there has been great interest in the use of so-called “structured abstracts”—abstracts that typically contain subheadings, such as “background,” “aims,” “methods,” “results,” and “conclusions.” Indeed, the early rise in the use of such abstracts was phenomenal [ 23 ], and it has no doubt continued to be so up to the present day. Evaluation studies have shown that structured abstracts are more effective than traditional ones, particularly in the sense that they contain more information [ 24–31 ]. However, a caveat here is that some authors still omit important information, and some still include information in the abstract that does not match exactly what is said in the article [ 32–35 ].

Additional research has shown that structured abstracts are sometimes easier to read and to search than are traditional ones [ 36, 37 ], but others have questioned this conclusion [ 38, 39 ]. Nonetheless, in general, both authors and readers apparently prefer structured to traditional abstracts [ 40–42 ]. The main features of structured abstracts that lead to these findings are that:

• the texts are opened-up and clearly subdivided into their component parts, which helps the reader perceive their structure;
• the abstracts sequence their information in a consistent order under consistent subheadings, which facilitates search and retrieval; and
• the writing under these subheadings ensures that authors do not miss out anything important.

Nonetheless, there are some difficulties—and these difficulties become more apparent after considering the structured abstracts of systematic reviews. First of all, the typographic practice of denoting the subheadings varies from journal to journal [ 43, 44 ]. Second, and of more relevance here, there is a range of subheadings used both within and among journals [ 45, 46 ], which militates against rapid retrieval. Table 4 shows an example of these variations by listing the subheadings used in the abstracts in just one volume of the Journal of the American Medical Association. Finally, it appears that some authors omit important subheadings or present them in a different order (e.g., reporting the conclusions before the results) [ 47 ].

Table 4 Different numbers of subheadings used in abstracts in the same volume of the Journal of the American Medical Association

The implications of these difficulties are that a decision needs to be made, based upon appropriate evaluation studies, about what are the key subheadings that can be used consistently in systematic reviews. The journal Evidence-Based Medicine, for example, uses the following six subheadings: “Question(s),” “Data sources,” “Study selection,” “Data extraction,” “Main results,” and “Conclusions,” but the Cochrane Handbook [ 48 ] recommends another seven: “Background,” “Objectives,” “Search strategy,” “Selection criteria,” “Data collection and analysis,” “Main results,” and “Reviewers' conclusions.” Presumably, these different sets of subheadings have developed over time with experience. For example, “Objective(s)” initially preceded “Question(s)” in Evidence-Based Medicine. In the future, refining these subheadings further may be possible by using appropriate typographic cueing, to separate important from minor subheadings, such as those headings used in the Journal of the American Medical Association. It will be essential, however, to use consistent terminology throughout the literature to aid both the creation of and retrieval from the abstracts of systematic reviews. Editors may consult their readers and their authors for possible solutions to this problem.

THE TYPOGRAPHIC SETTING FOR ABSTRACTS OF SYSTEMATIC REVIEWS

Early research on the typographic setting of structured abstracts in scientific articles suggests that the subheadings should be printed in bold capital letters with a line space above each subheading [ 49 ]. But this research has been done with structured abstracts that only have four subheadings. However, the abstracts of systematic reviews are likely to have more than four-subheadings—indeed, as noted above, six or seven seem typical. Also, some of these subheadings may be more important than others.

Generally speaking, there are two ways of clarifying the structure in typography. One is to vary the typography, the other to vary the spacing [ 50, 51 ]. In terms of typography, not overdoing is best; there is no need to use two cues when one will do. Thus, it may be appropriate to use bold lettering for the main subheadings and italic lettering for the less important ones, without adding the additional cues of capital letters or underlining. Also, as the subheadings appear as the first word on a line, placing a line space above them enhances their effectiveness, so there is no need to indent the subheadings as well. The abstracts published in the Cochrane Library follow this procedure.

Finally in this section, it should be noted that it is easier to read an abstract:

• that is set in the same type-size (or larger) than the body of the text of the review, unlike many journal abstracts, [ 52 ];
• that does not use “fancy'” typography or indeed bold or italic for its substantive text [ 53 ]; and
• that is set in “unjustified text,” with equal word spacing and a ragged right-hand margin, rather than in “justified text,” with unequal word spacing and straight left- and right-hand margins. This is particularly the case if the abstract is being read on screen [ 54 ].

CONCLUSIONS

The research reviewed above suggests that, in presenting the abstracts to systematic reviews, attention needs to be paid to their language, their structure, and their typographic design. Figure 1 shows a “before and after” example for a fictitious abstract for a systematic review. The purpose of this example is to encapsulate the argument of this paper and to show how changes in wording and typography can enhance the clarity of an abstract for a systematic review.

Acknowledgments

The author is indebted to Iain Chalmers, Philippa Middleton, Mark Starr, and anonymous referees for assistance in the preparation of this paper.

* Based on invited presentation at the VIIth Cochrane Colloquium, Rome, Italy, October 1999.

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Peer-reviewed

Research Article

Echogenic intracardiac foci detection and location in the second-trimester ultrasound and association with fetal outcomes: A systematic literature review

Roles Formal analysis, Investigation, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation National Centre for Population Health and Wellbeing Research, Swansea, United Kingdom

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing

Affiliation Swansea University, Sketty, Swansea, United Kingdom

Roles Data curation, Formal analysis, Writing – review & editing

Affiliation Cardiff University, University Hospital of Wales, Cardiff, United Kingdom

Roles Writing – review & editing

Affiliation Cardiff and Vale UHB: NHS Wales Cardiff and Vale University Health Board, Children’s Heart Unit, Cardiff, United Kingdom

Roles Formal analysis, Investigation, Methodology, Project administration, Visualization, Writing – original draft, Writing – review & editing

• Hope Eleri Jones, 
• Serica Battaglia, 
• Lisa Hurt, 
• Orhan Uzun, 
• Sinead Brophy

• Published: April 22, 2024
• https://doi.org/10.1371/journal.pone.0298365
• Peer Review
• Reader Comments

Echogenic Intracardiac Foci (EIF) are non-structural markers identified during the routine 18–20-week foetal anomaly ultrasound scan yet their clinical significance on future outcomes for the infant is unclear.

To examine the association between EIF and risk of preterm birth, chromosomal abnormalities, and cardiac abnormalities.

A review across four databases to identify English language journal articles of EIF using a cohort study design. All studies were reviewed for quality using the Critical Appraisal Skills Programme (CASP) checklist and data extracted for comparison and analysis.

19 papers from 9 different countries were included. Combining these studies showed 4.6% (95% CI = 4.55–4.65%) of all pregnancies had EIF which was on the left in 86% of cases, on the right in 3% of cases and bilaterally in 10%. There was no evidence that EIF was associated with higher rates of preterm birth. However, it is possible that infants with EIF were more likely to be terminated rather than be born preterm as there was a 2.1% (range 0.3–4.2%) rate of termination or death of the foetus after week 20 among those with EIF. There was no evidence that EIF alone is highly predictive of chromosomal abnormalities. There was evidence that EIF is associated with higher rates of minor cardiac abnormalities (e.g. ventricular septal defect, tricuspid regurgitation or mitral regurgitation)) with 5.1% (224 of 4385) of those with EIF showing cardiac abnormalities (3.08% in retrospective studies and 17.85% in prospective studies). However, the risk of cardiac defects was only higher with right-sided EIF and where the EIF persisted into the third trimester. However, this is a rare event and would be seen in an estimated 4 per 10,000 pregnancies.

EIF alone was not associated with adverse outcomes for the infant. Only persistent EIF on the right side showed evidence of carrying a higher risk of cardiac abnormality and would warrant further follow-up.

Citation: Jones HE, Battaglia S, Hurt L, Uzun O, Brophy S (2024) Echogenic intracardiac foci detection and location in the second-trimester ultrasound and association with fetal outcomes: A systematic literature review. PLoS ONE 19(4): e0298365. https://doi.org/10.1371/journal.pone.0298365

Editor: Mateen A. Khan, Alfaisal University, SAUDI ARABIA

Received: October 26, 2023; Accepted: January 24, 2024; Published: April 22, 2024

Copyright: © 2024 Jones et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: This is a literature review so the relevant data is in each of the papers mentioned in the review that are all open access. The values behind the measures reported and used to build graphs and figures are provided in the supplementary information .

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Congenital heart disease (CHD) is characterised by defects in the heart as it forms in the growing foetus [ 1 ]. CHD is the most common congenital abnormality in infants today with a diagnosis made 1 in every 100 births [ 2 , 3 ]. CHD is the leading cause of infant mortality [ 3 , 4 ]. Improvements in early detection and diagnosis would greatly improve the support and service provision for families when the infant is born, developing early preventative interventions, and putting in place enhanced monitoring and care for the infant.

A foetal anomaly scan is offered to all pregnant women in the UK between weeks 18-to-20 of pregnancy which includes routine screening for CHD [ 5 , 6 ]. However, it is estimated that only 50% - 75% of cases of serious congenital cardiac abnormalities are detected during this scan [ 5 ]. Potential discrepancies may be due to variations in equipment and facilities available to undertake the appropriate level of screening [ 7 ]. The extensive use and improvements to ultrasound imaging has enabled more detailed detection of fetal structural variations alongside the identification of more subtle non-structural findings, labelled as markers [ 7 – 9 ]. This has led to the identification of ultrasound soft markers (USM) [ 10 ], including Echogenic Intracardiac Foci (EIF), which are often discovered as an incidental finding during prenatal screening [ 11 ].

EIF have been described as small echogenic areas of microcalcification or fibrosis on the papillary muscle of either or both atrioventricular valves of the foetal heart [ 12 ]. EIF are often referred to as echo bright spots or hyper echogenicity of foetal soft tissue [ 13 , 14 ] when visualised on a foetal ultrasound. They are of equal or greater brightness than the surrounding bone [ 15 , 16 ]. The pathological cause of EIF remains ambiguous and it is still unclear what is the significance, if any, in terms of defects in the developing heart of the foetus. Research has suggested that EIF prevalence during this second-trimester scan is estimated to occur in between 0.17% and 20% of pregnancies [ 7 ]. The prevalence varies by race, with the highest incidence found amongst Asian populations [ 17 ].

Previous research has described EIF as often transient, resolving by the third trimester of pregnancy or after delivery [ 18 ], nonpathological or benign in isolation [ 11 ], and therefore has been highlighted that isolated soft markers may be present in 10% of normal foetuses [ 19 ]. However, multiple USM and the presence of specific soft markers, in terms of the specific location and size, may be associated with underlying chromosomal abnormalities (such as an association between the presence of EIF and a later diagnosis of Down’s syndrome) albeit the current evidence is not supportive of this [ 20 ] or adverse infant outcomes [ 21 ]. This suggests that the presence of specific soft markers may be associated with structural abnormalities and developmental conditions [ 22 ].

Given that EIF are small structures within the foetal ventricle chamber, they have been commonly associated with other soft markers [ 19 ]. However, it is unclear whether EIF can be used as a screening tool for cardiac heart diseases as previous research has shown mixed results. Despite the possible concerns surrounding the association between the development of structural and chromosomal abnormalities in the affected foetus, available data is debatable and inconclusive in some publications whilst others clearly showed no significance.

The presence of EIF with additional risk factors such as older maternal age (>35 years) places the mother in a high-risk category [ 22 ] during the pregnancy. Depending on the association with other soft markers this may lead to a referral for an echocardiogram and/or genetic counselling for amniocentesis to investigate possible chromosomal abnormalities. If EIF persists until birth and is present alongside other soft markers, a postnatal echocardiogram would be recommended and a referral to neonatal consultant. However, with increasing maternal age [ 23 ] and improvements in ultrasound detection [ 9 ] this is becoming more common therefore adding to costs of healthcare, potentially with little gain as the prevalence of congenital abnormality has remained constant [ 24 ].

It remains unclear whether EIF encompasses both benign transient structural variations and pathological changes [ 18 , 22 ]. Distinguishing between these two would be significant in terms of determining those to take forward for echocardiography and this is especially important in times of financial strain on the NHS. It is unclear whether location of EIF and number of EIFs are of more significance rather than their presence or absence.

The aim of this literature review is to examine the association between EIF and infant outcomes. Specifically: 1) The association between EIF identified at 18–20 weeks and risk of preterm birth, death, specific cardiac diagnosis (CHD) and chromosomal abnormalities. 2) The association between the number of EIF (single vs multiple), the location of EIF (left, right or bilateral) and the risk of preterm birth, death, cardiac diagnosis, and chromosomal abnormalities.

This review follows the Population-Interest-Comparator-Outcome (PICO) criteria to guide the scope and breadth of the literature review and set the inclusion criteria. The population was defined as the foetus at the 18–20-week ultrasound scan. The interest was where EIF was identified in the scan (as identified by the sonographer) compared to the comparator of those with no EIF. The infant outcomes include preterm delivery, death, structural cardiac abnormality, and chromosomal abnormalities.

Inclusion criteria

Peer-reviewed cohort studies in English, with full-text availability, published between 2013–2023. Studies included prospective and retrospective cohort studies with the assessment of EIF (with or without other markers) recorded by ultrasound at 18–20 weeks gestation and recording through follow-up (e.g., birth and post birth up to 5 years) with one of the outcome variables of interest. Studies which contain follow-up data to birth and infancy following assessment of routine ultrasound screening in a healthcare setting in the second trimester of pregnancy were included. Studies that only followed up EIF pregnancies without a comparison group were included in selected studies. However, if selection bias was present (e.g., only women >35 years) this was recorded in the data quality assessment and incorporated into the interpretation.

Exclusion criteria

Studies were excluded if the full text was not available in English, they examined non-cardiac echogenic focus (e.g. identified within the kidneys, liver, bowel, thyroid, hepatic, and pancreas). Also excluded were those not performed during the second-trimester ultrasound scan or those studies predicting echogenic foci as the outcome rather than the exposure.

Outcome measures

The primary outcome measure is preterm birth (before 37 weeks) or death of the foetus. Secondary outcomes include chromosomal abnormality (genetic testing for aneuploidy, amniocentesis or NIPT (Non-Invasive Prenatal testing) reports) and cardiac abnormality (fetal echocardiology reports and/or postnatal diagnosis).

Literature search

The literature search was carried out in three stages: Stage one was an initial search on Pubmed to identify the index terms which best identify relevant articles. This initial search used the first 10 relevant primary studies and collated the search terms that were used. The second stage took these updated search terms to apply to the; Web of Science online tool which searches the following databases: Web of Science Core Collection, BIOSIS Citation Index, Current Contents Connects, Data Citation Index, Derwent Innovations Index, and MEDLINE (Medical Literature Analysis and Retrieval System Online). This search was repeated on Pubmed and Scopus individually. The final stage reviewed the reference list of the included studies and reviews in the area. Grey literature was also reviewed including the National Congenital Heart Disease Audit (NCHDA). The literature search was carried out in June 2023 and imported onto Covidence software [ 25 ]. The keywords identified for the initial search included: Echogenic intracardiac foci, Chromosomal abnormalities, Prenatal diagnosis, Ultrasonography, Echocardiography, Pregnancy trimester second, Foetal cardiac anomalies OR foetal cardiac abnormalities, Foetal echocardiography, Foetal heart, Trisomy 21 (Down syndrome), Prenatal screening and Pregnancy outcomes. The search terms used to identify relevant papers consisted of four concepts and were combined to form the following search string across all key databases: “echogenic intracardiac foc*” OR “echogenic foc*” OR “intracardiac foc*” OR “cardiac echogenic foc*”.

Study selection

Covidence automatically removes duplicate records [ 25 ]. Initial screening based on the title and abstract was carried out by two independent reviewers based on the inclusion and exclusion criteria. For those publications selected to take forward, a second screening based on the full text was conducted and those selected as relevant were taken forward to data extraction ( Fig 1 ).

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Extraction of relevant variables

A data extraction form was designed which included the Critical Appraisal Skills Programme (CASP) quality review [ 26 ] to assess risk of bias. Quality was assessed to include methods of addressing confounding variables, quality of measurement of outcome and exposure and if outcomes by exposure and loss to follow-up. The data includes study identification (number, first author), study demographic information (country, size of study, study design), total number of pregnancies, number with EIF recorded, duration of follow up, recording of outcomes of interest, position (left/right) of EIF and number of EIF (single/multiple). See the supplementary information for details of extracted variables, definitions and how they were recorded ( S1 Table ).

Comparison data

The outcomes for those with no EIF were recorded in the same way as those with EIF reporting the number of preterm births, deaths, congenital abnormalities and cardiac abnormalities.

There were 243 non-duplicate studies that were identified using the search criteria. Of these, 206 were excluded at the title and abstract screening due to studies being published before 2013, not a study examining EIF (e.g., assessing cysts or other soft markers) and non-English studies. 35 full journal articles were reviewed. However, the majority were excluded on the basis that they did not have a cohort design (health economics study or case study or case series), did not have follow-up of those with EIF, or did not have follow up of the outcomes which were considered within this review. After full text review, 19 studies were included ( Fig 2 ). These 19 studies covered 9 different countries with 9 of the studies from China, 2 from Iran and 2 from Pakistan. The smallest study had a follow-up of 7 EIF pregnancies and the largest was 143,067 pregnancies of which 2647 had EIF. 6 studies had prospective follow-up of infants and the remaining 13 had retrospective follow-up using routine medical records.

https://doi.org/10.1371/journal.pone.0298365.g002

The majority of studies were rated as being of moderate quality as there was missing data, or loss to follow-up, especially in the prospective studies. For example, a postpartum follow-up study was performed on women referred for echocardiography and of these 7 had EIF [ 1 ]. This study was rated as high risk of selection bias and so rated moderate. Another study was rated moderate as there was loss to follow-up among some EIF participants [ 27 ]. Other studies were not stratified by EIF characteristics making interpretation difficult and therefore rated low [ 28 ]. Moreover, in some cases the dates of recruitment were not being reported, and it was unclear how many terminations of pregnancies occurred [ 29 ]. Overall, the study quality was rated as moderate and there was a risk of bias such as loss to follow-up or selection bias in various papers.

EIF association with outcomes

This review followed 34,104 women from 19 studies (4 studies did not provide a total number of women screened). Of these, there were 15,600 EIFs or 4.6% (95% CI = 4.55–4.65%) of all pregnancies and 4.5% (range 0.5% to 17.8%) of pregnancies when the EIF proportion of each study was averaged. This highlights that EIF is a relatively common finding on ultrasound scans. In addition, 5 studies followed-up those with EIF only (e.g. a cohort of those with EIF) which identified an additional 1,400 EIFs for follow-up. On average, 26.6% presented with multiple EIFs and the remaining had a single EIF. Taking the averaged levels in each study (6 studies reporting the location of EIF), the EIF was on the left side in 86% of cases, on the right in 3%, and bilaterally in 10%. Therefore, EIF on the right is a rare occurrence that only occurred in 13% of EIFs or 6 per 1000 pregnancies.

Preterm births

Five studies reported the rates of preterm birth where the prevalence was 7.2% (range 2–13%). This rate is comparable to the UK where the preterm rate is 7.8% (23) compared to 13% in North Africa [ 30 ] In two studies that reported preterm rates among non-EIF pregnancies, the range was between 5–20%. Comparing the two papers that reported EIF and non-EIF preterm rates, there was no evidence that EIF is associated with preterm birth with 4.8% (EIF) versus 5.1% (non-EIF) in Wales with the sample size 18,841 EIF (N = 858) [ 31 ], and 13.0% (EIF) versus 20.9% (non-EIF) [ 32 ] with the sample size 9,270 (EIF = 230) in Lebanon. This follow-up in a total of 5 studies (2 with control data) does not provide evidence of higher preterm rates in those with EIF. However, in the study in the UK [ 31 ], the authors had the scans reviewed by a quality assurance panel and of the 858 EIF scans only 615 were assessed by the quality assurance panel as EIF’s. This means that there were 44 preterm births out of 615 with EIF (7.2%) which is in line with population level preterm rates in Wales [ 23 ]. The non EIF was 921 preterm births out of 18,226 pregnancies without EIF (5.1%).

However, it is possible that infants with EIF were more likely to be foetal deaths or termination rather than being born preterm. There was a 2.0% (range 0.3–4.2%) rate of termination or death of the foetus after week 20, among those with EIF. This rate is higher than previously reported [ 33 ] which suggests that less than 0.5% of pregnancies will end in foetal death after 20 weeks. The main cause of death in China and Iran appears to be termination due to suggested chromosomal abnormalities and other soft markers. For example, pregnancies were terminated due to abnormal chromosome numbers (35)(28) and 50% of deaths had chromosomal abnormalities [ 19 ]. Many pregnant women with EIF had invasive foetal testing to screen for chromosomal abnormalities [ 28 ]. The findings presented that the increase in the risk of chromosomal abnormalities in the foetus was related to the pregnant women belonging to high-risk groups, rather than EIF [ 28 ].

In Wales, foetal deaths (0.48% of confirmed EIF pregnancies) were due to stillbirths and induced or spontaneous pregnancy loss. This rate of foetal death is in line with expected rates and comparable to non-EIF rates. In Lebanon, foetal deaths (0.9%) were due to foetal demise but this was at the expected rate and equivalent to non-EIF foetal loss rates. In Pakistan, the deaths were associated with cases of pulmonary artery hypertension and tetralogy of Fallot and were all neonatal deaths ( Fig 3 ). This was a higher-than-expected rate, but the sample size was small.

https://doi.org/10.1371/journal.pone.0298365.g003

Overall, there was no evidence that preterm rates were higher among those with EIF. Terminations were higher in China and Iran, and these were associated with chromosomal abnormalities. The rate of foetal death was not higher in countries like Wales or Lebanon with different health care practices and where invasive foetal testing is not performed when EIF is detected.

Chromosomal abnormalities

Ten studies [ 18 , 19 , 22 , 27 , 31 , 32 , 34 – 37 ] reported chromosomal abnormalities and the rate of abnormalities was 1.98% (range 0–5.7%) among those with EIF. The chromosomal abnormalities identified with EIF were Trisomy 18, 46, 21 XXY, XYY and Turner’s syndrome. Three studies also reported abnormalities among those without EIF and in each of these studies the internal comparison of abnormality rate between EIF and non-EIF suggested no higher rate of chromosomal abnormalities among those with EIF ( Fig 4 ). The sample size of EIF pregnancies were 58 in Ko et al. [ 22 ], 1099 in Wang et al. [ 18 ] and 230 in Mirza et al. [ 32 ].

https://doi.org/10.1371/journal.pone.0298365.g004

Cardiac abnormalities

Cardiac abnormalities were reported in 10 studies [ 1 , 3 , 14 , 15 , 27 , 34 , 37 – 39 ] and the average for all studies was 8.2% (range 1.8% to 39%). When all findings were combined there was a 5.1% rate (224/4385) ( Fig 5 ). The retrospective cohort study findings gave a rate of 3.3% and the prospective studies (with higher rates of missing data and loss to follow-up) was 17.85%. Abnormalities included VSD, tricuspid regurgitation and mitral regurgitation. Two studies reported cardiac abnormalities in non-EIF pregnancies, which ranged from 1.5–3.1%. CHD is thought to affect about <1% of births [ 40 ]. There does appear to be evidence that EIF is associated with higher rates of cardiac abnormality (e.g. 3.3% (95%CI 1.1–5.6) rate of cardiac abnormality). However, it remains that 97% of those detected with EIF will not have a cardiac abnormality. Specific findings from the included studies are available in the supplementary information ( S2 Table ).

https://doi.org/10.1371/journal.pone.0298365.g005

Location of EIF

The location of the EIF was recorded in 6 studies. However, follow-up of proportion with a cardiac abnormality by EIF location was only recorded in three studies [ 14 , 15 , 39 ]. Combining the findings for left EIF compared to right EIF showed 7.9% (6/76) (95% CI: 2.9%-16.4%) of right EIF were associated with cardiac abnormality compared to 3.6% (107/2,992) (95% CI: 2.9%-4.3%) in the left (difference: 4.3% (95%CI: 0.03% to 12.6%)) showing higher rates with right-sided EIF compared to the left [ 14 , 15 , 39 ]. The rate of abnormality in bilateral EIF did not differ from the rate seen in the left EIF. The findings from Chiu [ 39 ] suggested persistent EIF into the third trimester may be associated with higher risk of congenital heart defects such as VSD. Therefore, the follow up of EIF later in pregnancy may be useful to examine if the EIF resolves or persists.

In summary, a EIF in the right ventricle may not resolve as often as that in the left and combining the findings from studies suggested that an EIF in the right is associated with higher rates of cardiac abnormality (7.9% rate if EIF at 20 weeks but this could be higher if persistent beyond 20 weeks). There is ethnic variation in the prevalence of EIF and therefore there is likely to be ethnic variation in the significance of EIF. Only an EIF observed in the third trimester on the right may be associated with cardiac abnormality. However, this would be only 4 per 10,000 pregnancies who would have a right EIF which did not resolve by the third trimester (e.g. 4.5 pregnancies have an EIF, 3% of these are on the right (13.5 per 10,000) and of these 30% persist to third trimester or 4 per 10,000 pregnancies have a persistent EIF on the right). Therefore, EIF in general, is unlikely to be significant as a predictive or screening tool.

Findings from this review highlight that only if the EIF is on the right side and persists until the third trimester, is there a higher chance of cardiac abnormalities (7% risk of cardiac abnormality at 20-week scan), and only in these persistent cases could it be advised that there should be further investigation. This finding that the EIF is not predictive of poor outcomes is significant, especially given the current post COVID-19 strains on health systems worldwide. It must be noted that this data is for isolated markers. There is clear and consistent data that multiple markers are associated with adverse outcomes.

Supportive evidence in terms of the risk of aneuploidy reported that isolated EIF is considered an incidental finding and does not warrant amniocentesis, but that amniocentesis should be undertaken in high-risk cases where other soft markers are identified or there is a history of chromosomal abnormalities in previous pregnancies [ 38 ]. A meta-analysis for the risk of Down’s Syndrome suggests that EIF increases the risk by 5–7 folds [ 41 ]. In contrast, an association between EIF and Trisomy 21 is not always reported [ 42 ]. The Society for Foetal Medicine [ 17 ] recommends that for those with no previous aneuploid screening and have an isolated EIF, there should be genetic counseling to estimate the probability of Trisomy 21 and discussion on options for non-invasive screening.

Findings from this review suggest that an isolated EIF would not warrant further investigation, that multiple foci do not carry a higher risk compared to single foci, and that recommendations to follow-up should be based on other risk factors (e.g., maternal age, family history) rather than the presence of EIF without other soft markers. It was found that there were higher terminations in countries like China where many pregnant women with EIF have invasive tests to screen for abnormalities. This suggests that EIF in these countries may be randomly associated with or a consequence of chromosomal abnormalities rather than being a marker for it or that simply the perceived risk of future abnormalities is enough to lead to a termination. The majority of infants terminated in these studies had Variants of Uncertain Significance (VOUS) and so may have been healthy. In countries where the presence of EIF does not lead to chromosomal testing there was no evidence of higher rates of death among infants with EIF. In low-risk pregnancies with EIF, invasive chromosomal testing may lead to harm, such as an increased abortion rate, and is unlikely to lead to benefits of increased detection of chromosomal abnormalities.

VSD was associated with EIF in some studies [ 1 , 14 , 15 , 27 , 29 , 34 , 38 , 39 ] but this association can also be random and non-causative or consequential. VSD is the most common congenital heart defect in children [ 15 , 27 , 41 , 43 , 44 ]. These often resolve and close spontaneously when the baby is born due to the reversal of vascular resistance at birth. Studies have suggested that overall cardiac function may not be affected by the presence of an isolated EIF when assessed by conventional echocardiography and Tissue Doppler (TD) imaging [ 45 ]. Therefore, in isolation, an EIF may not warrant future follow-up. Previous studies have found an association between the presence of an EIF and the incidence of mitral/tricuspid regurgitation. However, it has been suggested that care needs to be taken when assessing if this is true colour flow generated by atrioventricular valvular regurgitation jets or in fact colour Doppler twinkling artefact (which causes a rapidly changing combination of red and blue complexes behind the EIF which may mimic flow) [ 46 ]. Transient and mild valvular regurgitation can also be seen in fetuses with no cardiovascular anomaly and can be transient and without pathological significance [ 47 ]. Previous research has confirmed rough surfaces, such as that created by microcalcifications or mineralisation in the papillary muscle (which is what EIF is suggested to be) [ 48 , 49 ] is seen to reflect the ultrasound incidence beam and increase pulse duration of received radiofrequency. This may be misinterpreted as movement with the atrioventricular valve when visualised on a foetal echocardiogram [ 46 ]. Finally, the work by Hurt et al. [ 31 ] showed that when the EIF’s were taken to a quality assessment panel, 30% were not confirmed as EIF and were removed from the research analysis. Therefore, the identification of EIF has poor inter-rater reliability.

That there is a link between EIF and cardiac abnormality is supported by Taksande et al. [ 50 ] who recently published a systematic review and meta-analysis and found a prevalence of 4.8% among studies published between 1987–2021. This is comparable to our finding which included 7 of the same studies (but not a meta-analysis) from 2013–2023. The Taksande [ 50 ] analysis did not look at left vs right EIF and did not compare with those without EIF. Our findings suggest, when compared to those without EIF in the same study, only a right sided EIF carries significantly higher risk of cardiac abnormality. A follow-up study by Hurt et al. [ 51 ] published 2023, which followed up the infants with EIF and without EIF for 10 years found no evidence of association of EIF with cardiac admissions or diagnosis of cardiac abnormalities but did find an increased risk of respiratory admissions (Hazard ratio 1.27 (95% CI: 1.04–1.54)). The Hurt study did not look at left vs right EIF but the association with respiratory conditions may support the hypothesis that right sided EIF carries morbidity risk more than left sided EIF.

Strengths and limitations

This work was able to examine outcomes from 15,600 EIFs and reported that EIF at 20 weeks is not significant as a screening tool in pregnancy for infant outcomes at birth. The review covered nine different countries so provides assessment of outcomes for infants of different ethnicities and thus is generalisable. However, the finding that EIF on the right side could carry a 7% risk of cardiac abnormality was based on only two studies and a total of 76 EIFs on the right side. This represents a small sample size which displays high variability in terms of the likelihood of cardiac abnormality (2.9% to 16.9%). An additional study [ 52 ], which was excluded as it was considered that the years of recruitment overlapped with Chiu, 2019 [ 39 ] and so some pregnancies may be replicated in both papers, found a significantly higher prevalence of congenital heart defect in the right ventricle (14.8%, n = 4 cases) compared to left (2.8%, n = 18 cases) (p = 0.0146). In this paper the cases of congenital heart defect were confirmed by postnatal echocardiography and 16.7% (4/24) chose termination of pregnancy upon detection of structural defect. Absence of prospective and contemporary data in the Western world owing to diminished attention to benign EIF may have caused an unintended bias towards ethnic disparity in the current analysis.

This review was not able to examine the risks of persistent right EIFs, which are likely to affect fewer infants but have a higher likelihood of cardiac abnormality. In addition, the variation in studies from different countries means that combining study outcomes to a single score may be prone to error, in terms of concealing the variation which may exist between different ethnic groups.

The studies included in this review used different health care systems and therefore may not be comparable in their definition and identification of adverse infant outcomes. Combining the findings from different studies may also create errors and biases as there is no harmonisation in their definitions of the outcomes. The studies undertaking prospective analysis were prone to missing data and skewed data collection e.g., only those families who returned for assessment were included. Therefore, the prospective studies were rated as weaker and prone to bias compared to the retrospective studies.

The screening process and review was conducted by two independent reviewers performing the extraction in parallel and then comparing decisions to reduce bias. The review benefited from the use of specialist software Covidence to undertake the review [ 25 ]. It allows screening to be more efficient and easily tracked. The date restriction of the last 10 years was justified due to improvements in ultrasound technology in recent years. However, this exclusion criteria may have meant that important previous research was missed.

Recommendations

Persistent EIF in the right side should be investigated using an echocardiogram. There are limited cases and this could help predict cardiovascular abnormality as there is a higher prevalence in this group. However, there is no justification to follow up EIFs on the left and especially those in isolation with no other markers detected. Any recommendation of follow-up would be based on other risk factors such as multiple other soft markers or family history, rather than the presence of an EIF.

This review did not examine the long-term follow-up of infants with EIF and it is possible that persistent EIF could be associated with adult conditions such as VSD or valve regurgitation. Future investigation into failure to thrive, a possible audible murmur, or symptoms such as breathlessness in an infant, may identify longer term adverse outcomes associated with EIF.

Conclusions

In conclusion, we examined the outcomes from 19 studies and present that left sided EIFs are not predictive of poor foetal outcomes, and studies reviewed here suggested these are often transient and resolve with time. Persistent EIF on the right side, which is a rare event in itself, would warrant follow-up. This information is beneficial for pregnant women, families, and clinicians to facilitate the development of appropriate clinical guidelines and care pathways during pregnancy and after birth, including the appropriate use of medical interventions and treatment.

Supporting information

S1 table. extracted variables, definitions and how they were recorded..

https://doi.org/10.1371/journal.pone.0298365.s001

S2 Table. Specific findings from included studies which examine cardiac outcomes.

https://doi.org/10.1371/journal.pone.0298365.s002

https://doi.org/10.1371/journal.pone.0298365.s003

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• Case Report
• Open access
• Published: 22 April 2024

A loss-of-function AGTR1 variant in a critically-ill infant with renal tubular dysgenesis: case presentation and literature review

• Aljazi Al-Maraghi 1 ,
• Waleed Aamer 1 ,
• Mubarak Ziab 2 ,
• Elbay Aliyev 1 ,
• Najwa Elbashir 1 ,
• Sura Hussein 1 ,
• Sasirekha Palaniswamy 1 ,
• Dhullipala Anand 3 ,
• Donald R. Love 4 ,
• Adrian Charles 5 ,
• Ammira A.S.Akil 2 &
• Khalid A. Fakhro 1 , 2 , 6 , 7  

BMC Nephrology volume  25 , Article number:  139 ( 2024 ) Cite this article

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Metrics details

Renal tubular dysgenesis (RTD) is a severe disorder with poor prognosis significantly impacting the proximal tubules of the kidney while maintaining an anatomically normal gross structure. The genetic origin of RTD, involving variants in the ACE, REN, AGT, and AGTR1 genes , affects various enzymes or receptors within the Renin angiotensin system (RAS). This condition manifests prenatally with oligohydramninos and postnatally with persistent anuria, severe refractory hypotension, and defects in skull ossification.

Case presentation

In this report, we describe a case of a female patient who, despite receiving multi vasopressor treatment, experienced persistent hypotension, ultimately resulting in early death at five days of age. While there was a history of parental consanguinity, no reported family history of renal disease existed. Blood samples from the parents and the remaining DNA sample of the patient underwent Whole Genome Sequencing (WGS). The genetic analysis revealed a rare homozygous loss of function variant (NM_000685.5; c.415C > T; p.Arg139*) in the Angiotensin II Receptor Type 1 ( AGTR1 ) gene.

This case highlights the consequence of loss-of-function variants in AGTR1 gene leading to RTD, which is characterized by high mortality rate at birth or during the neonatal period. Furthermore, we provide a comprehensive review of previously reported variants in the AGTR1 gene, which is the least encountered genetic cause of RTD, along with their associated clinical features.

Peer Review reports

Renal tubular dysgenesis (RTD) (MIM# 267,430) is a rare autosomal recessive disorder of renal tubular development that was first characterized in two stillborn siblings in 1983 [ 1 ]. The disease carries a poor prognosis and a high mortality rate due to the severity of the disease where patients may die in utero or soon after birth, despite the availability of high-quality clinical care. Although the exact prevalence of RTD is unknown, there are multiple reports of RTD cases [ 2 , 3 ].

The underlying pathophysiology of RTD involves reduced intrauterine renal perfusion leading to dysgenesis of proximal tubule formation in the kidneys, with preservation of grossly normal kidney structure [ 4 ].The clinical manifestations of RTD include persistent fetal anuria with subsequent oligohydramnios in pregnancy, pulmonary hypoplasia, and skull ossification defects of the bone due to persistent hypotension [ 5 ]. In addition, typical pathological changes seen on kidney sections taken from affected patients show the incomplete development of renal proximal tubules. These changes are attributed to the consequences of hypoperfusion and renal ischemia in the absence of Angiotensin II (ANG II) production or function, a defect responsible for the severe refractory hypotension observed at birth [ 6 ].

Previous studies have demonstrated the fundamental role of Renin Angiotensin System (RAS) during fetal development of the kidneys. Physiologically, the RAS pathway regulates extracellular fluid volume and maintains blood pressure levels in the body [ 7 ]. Several variants in four different genes encoding RAS signaling proteins ( AGT , REN , ACE , and AGTR1 ) have been described to cause RTD [ 8 ]. Variants in the AGTR1 gene constitute approximately 8% of the reported mutations causing RTD [ 9 ].

The Angiotensin II Receptor Type 1 ( AGTR1 ) gene encodes a receptor protein of the ligand angiotensin II, which is a potent vasopressor hormone in the RAS pathway [ 10 ]. The binding of ANG II to the Angiotensin II Type 1 receptor (AT1 receptor) promotes its activation, leading to vasoconstriction, sympathetic activity and aldosterone release from adrenals, ultimately increasing blood pressure [ 11 ]. Angiotensin II also regulates renal growth during fetal development [ 12 ].

Herein, we report a rare nonsense variant in the AGTR1 gene detected through whole genome sequencing (WGS) in a neonate exhibiting persistent anuria and resistant refractory pulmonary hypoplasia, ultimately resulting in early lethality.

The female patient, born to consanguineous parents (first degree cousins) with a family history of Oculocutaneous Albinism in the mother. This was the mother’s first pregnancy and antental ultrasound scans revealed oligohydramnios and Intra-Uterine Growth Retardation (IUGR). The patient was born prematurely at 36 weeks through an emergency cesarean section due to reduced fetal movement and failed induction. The baby was born weighing 2.0 kg with meconium stained liquor and Apgar scores were 6 and 9 at one and five minutes, respectively. The baby required minimal resuscitation and she was managed on continuous positive airway pressure (CPAP) in the first hour of life; however, within a few hours she deteriorated with bilateral pneumothoraces requiring chest drains, intubation, and ventilation. The patient was started on inhaled nitric oxide for hypoxic respiratory failure, and inotropes due to low blood pressure including dopamine, dobutamine, and epinephrine. The patient remained hypotensive with a mean blood pressure of 15–20 mmHg, which required the addition of hydrocortisone followed by vasopressin to improve her blood pressure. Her oxygen saturation measurements were 35%—45% in 100% FiO 2 . Supportive measures, including sedation, antibiotics, and fluids were administered. The patient didn’t have any urine output and she developed persistent hypoxia and hypotension, necessitating veno-arterial Extra Corporeal Membrane Oxygenation (ECMO) support on the second day of life, which led to an improvement in her oxygen saturation. However, the patients blood pressure remained low despite the ECMO and continuous inotropic support. While on ECMO, renal replacement therapy (CRRT) was initiated, effectively normalzing the creatinine levels, however the CRRT was discontinued due to the development of hypotension, resulting in progressive edema and fluid overload. Subsequently, the decision was made to decannulate and remove the ECMO support due to a substantial right-sided parenchymal hemorrhage and extra-axial hemorrhage observed on head ultrasound. The patient experienced coagulopathy, manifesting as oozing from the skin and chest tubes requiring multiple Fresh Frozen Plasma (FFP), cryoprecipitate, and red cell transfusions due to low hemoglobin, persistent thrombocytopenia and coagulopathy. On the fourth day, a multi-disciplinary team meeting, with the patient’s parents present, concluded to transition the patient from intensive care to comfort care with no further resuscitation. The patient was extubated the following day and passed away a few hours later.

Imaging studies that were done on the baby included: (1) Echocardiography, which showed a structurally normal heart but was associated with severe persistent pulmonary hypertension of newborn (PPHN) and complete right to left shunting across the ductus arteriosus; (2) Abdominal ultrasound, which showed non-specific bilateral echogenic kidneys; (3) Head ultrasound, which showed large left intra-parenchymal and extra-axial acute bleeding associated with mass effect.

The post-mortem examination revealed mildly hypoplastic kidneys, moderate pulmonary hypoplasia, solid and poorly aerated lungs with diffuse alveolar damage, significantly reduced skull vault mineralization and bony development, indicative features of oligohydramnios sequence. Limbs exhibited some flexion changes, and there were characterestics findings of of Potters’ facies, marked edema, and a structurally normal heart. Histopathology showed changes of renal tubular dysgenesis with the renal cortex containing crowded glomeruli separated by small tubules with distal tubular morphology and absence of proximal tubules (Fig.  1 ). The proximal tubules should be as numerous as the glomeruli and have plump lining cells with abundant cytoplasm. The medulla appeared largely unremarkable. The family history of parental consanguinity and the severity of symptoms prompted enrolling the family in the Mendelian disease program at Sidra Medicine (Fig.  2 a) [ 13 ]. Genome sequencing was performed on all family members, and following our in-house analysis pipeline [ 14 ], the patient was, initially, found to carry six de novo and nine homozygous rare protein-altering variants, including two that were predicted to lead to loss-of-function (LoF) (Additional file 1 ). These two include a variant in OR1J4 (c.221C > G, p.Ser74*), an olfactory receptor gene not known to be associated with Mendelian disease, and a nonsense previously unreported variant (NM_000685.5; c.415C > T; p.Arg139*) was identified in the Angiotensin II Receptor Type 1 (AGTR1) gene (Table  1 ). Importantly, LoF variants in this gene have been associated with renal tubular dysgenesis (MIM# 267,430) [ 8 ]. Both parents were heterozygous carriers of the variant (Fig.  2 b) and in-silico pathogenicity scores predicted it to be highly damaging (CADD of 39 and GERP of 5.8).

Renal histological characteristics. a H&E renal cortex, showing crowding of the glomeruli, with intervening tubules mainly of distal tubule type, and lack of proximal tubules. b CD10 highlighting the glomeruli and the Bowmans capsule, but normal proximal tubules are not seen, only weak staining of the ureteric buds

Patient characteristics and genetic findings. a Family pedigree of the patient along with genotypes of the nonesense AGTR1 variant (c.415C > T; p.Arg139*). b Chromatogram of Sanger sequencing showing the variant position and genotypes of the 3 family members. c Schematic of AGTR1 gene body with highlights of protein domains and reported ClinVar variants. The yellow stars refer to the staring system of ClinVar which indicate the review status of the variant

Discussion and conclusion

The molecular mechanisms underlying the genetic basis of RTD pathogenesis are still not fully elucidated; however, LoF/structural variants in genes encoding components of the RAS pathway are a major cause of the disease [ 8 ]. Disruption of the RAS leads to defects in the differentiation of proximal tubules during fetal development resulting in severe symptoms during pre- and postnatal periods including fetal anuria and oligohydramnios [ 15 ].

In this report, we present a case of a newborn female patient who suffered from congenital RTD and several severe complications, ultimately resulting in perinatal death at five days of life. Genetic analysis of the child and her parents identified a pathogenic nonsense variant in exon 3 of the AGTR1 gene. The predicted effects of this variant are protein truncation and possibly nonsense-mediated mRNA decay. To date, only eight RTD patients, including ours, have been reported with five different AGTR1 gene variants (Table  1 , Fig.  2 c), reflecting the rare nature of RTD and the significance of RAS signaling pathway in early development.

The genetic association of AGTR1 variants with an RTD phenotype is supported by the literature in which patients suffer severe symptoms during pre-and/or postnatal life [ 8 , 9 ]. In addition, recent evidence has pointed to the possibility of a milder form of the RTD depending on the variant position in the AGTR1 gene [ 16 ]. A male carrier of a homozygous LoF variant (p.Arg216*) in AGTR1 has been described who lived to 28 years of age under management with high doses of fludrocortisone which, along with vasopressin, have proved effective in managing RTD [ 16 ]. Overall, although the severity of symptoms in patients who carry AGTR1 mutations is consistent across all reported cases, it has been suggested that, similar to other genetic renal diseases, the phenotype is more severe when the affected protein is located more distally along the RAS pathway [ 17 ].

Reaching a final diagnosis of RTD prenatally has been challenging because all prenatal symptoms of oligohydramnios, and IUGR are not specific. This challenge leaves genetic testing as the only viable diagnostic option after none genetic causes have been excluded [ 18 ], particularly when offered in the context of prenatal diagnosis through chorionic villus sampling. Even when early symptoms began to emerge postnatally, the patient's instability did not indicate a specific diagnosis. The genetic finding complemented by the histopathology confirmed the diagnosis of RTD. Although the treatment remained supportive, providing prompt answers to healthcare providers and families is immensely valuable.

Given the severity of the condition, improved outcomes for RTD patients can be realized through early detection, facilitating clinical decision making and enhancing neonatal care, particularly in cases of severe congenital diseases with prenatal indications and symptoms. Genetic testing empowers carrier parents to make informed decisions regarding their future family plans. In the case of the newborn discussed here, the parents received appropriate counselling and were informed about the genetic results, and the disease risk in subsequent pregnancies. Early identification of recessive pathogenic variants, particularly in such highly consanguineous population, plays a pivotal role in the success of population screening programs and contributes to lowering the long-term burden of Mendelian diseases.

Availability of data and materials

The datasets analysed during the current study are available in the Genome Sequence Archive in Sidra Medicine, Qatar. Variant submitted in ClinVar under accession number VCV002430252.2.

Abbreviations

Angiotensin-converting enzyme

Angiotensin II Receptor Type 1

Continuous positive airway pressure

Renal replacement therapy

Extra Corporeal Membrane Oxygenation

Intra-uterine growth retardation

Persistent pulmonary hypertension of newborn

Renin angiotensin system

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Acknowledgements

We are grateful to the families and individuals who participated in this study.

This work was supported by Qatar Foundation, National Priorities Research Program (NPRP11S-0110–180250).

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Aljazi Al-Maraghi, Waleed Aamer, Elbay Aliyev, Najwa Elbashir, Sura Hussein, Sasirekha Palaniswamy & Khalid A. Fakhro

Department of Human Genetics-Precision Medicine in Diabetes Prevention, Sidra Medicine, P.O. Box 26999, Doha, Qatar

Mubarak Ziab, Ammira A.S.Akil & Khalid A. Fakhro

Neonatology Division, Sidra Medicine, P.O. Box 26999, Doha, Qatar

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Khalid A. Fakhro

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Contributions

A. A. conducted genetic analysis and literature searches, taking the lead in writing the manuscript. W. A. played a key role in Whole Genome Sequence acquisition and manuscript drafting. A. D. contributed to clinical data collection and provided support to the patient. M. Z. and D. R. L. performed variant validation, while J. L. and S. H. were involved in patient enrollment and sample processing. E. A. performed structural variant analysis and reviewed the manuscript. D. R. L. offered clinical interpretation of genetic findings, and S. P. managed follow-up and reporting. A. C. provided images and description of renal histopathology. A. A. K. oversaw the original study, supervised patient recruitment, and handled manuscript review, editing, and regulatory requirements. K. A. F. secured funding, designed the study, coordinated the overall process, and conducted final proofreading and critical manuscript review. All authors participated in reading and approving the final manuscript.

Corresponding author

Correspondence to Khalid A. Fakhro .

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Ethics approval and consent to participate.

The institutional review board approval of this study was obtained from Sidra Medicine, Qatar (IRB 1636872). Furthermore, the family members signed informed consent and assent forms to participate in the proposed research study.

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We obtained written informed consent from the patient’s father to publish this potentially identifiable information from all of the family members included in this case report.

Competing interests

The authors declare no competing interests.

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Al-Maraghi, A., Aamer, W., Ziab, M. et al. A loss-of-function AGTR1 variant in a critically-ill infant with renal tubular dysgenesis: case presentation and literature review. BMC Nephrol 25 , 139 (2024). https://doi.org/10.1186/s12882-024-03569-z

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DOI : https://doi.org/10.1186/s12882-024-03569-z

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• Volume 33, Issue 5
• Equitable and accessible informed healthcare consent process for people with intellectual disability: a systematic literature review
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• http://orcid.org/0000-0002-8498-7329 Manjekah Dunn 1 , 2 ,
• Iva Strnadová 3 , 4 , 5 ,
• Jackie Leach Scully 4 ,
• Jennifer Hansen 3 ,
• Julie Loblinzk 3 , 5 ,
• Skie Sarfaraz 5 ,
• Chloe Molnar 1 ,
• Elizabeth Emma Palmer 1 , 2
• 1 Faculty of Medicine & Health , University of New South Wales , Sydney , New South Wales , Australia
• 2 The Sydney Children's Hospitals Network , Sydney , New South Wales , Australia
• 3 School of Education , University of New South Wales , Sydney , New South Wales , Australia
• 4 Disability Innovation Institute , University of New South Wales , Sydney , New South Wales , Australia
• 5 Self Advocacy Sydney , Sydney , New South Wales , Australia
• Correspondence to Dr Manjekah Dunn, Paediatrics & Child Health, University of New South Wales Medicine & Health, Sydney, New South Wales, Australia; manjekah.dunn{at}unsw.edu.au

Objective To identify factors acting as barriers or enablers to the process of healthcare consent for people with intellectual disability and to understand how to make this process equitable and accessible.

Data sources Databases: Embase, MEDLINE, PsychINFO, PubMed, SCOPUS, Web of Science and CINAHL. Additional articles were obtained from an ancestral search and hand-searching three journals.

Eligibility criteria Peer-reviewed original research about the consent process for healthcare interventions, published after 1990, involving adult participants with intellectual disability.

Synthesis of results Inductive thematic analysis was used to identify factors affecting informed consent. The findings were reviewed by co-researchers with intellectual disability to ensure they reflected lived experiences, and an easy read summary was created.

Results Twenty-three studies were included (1999 to 2020), with a mix of qualitative (n=14), quantitative (n=6) and mixed-methods (n=3) studies. Participant numbers ranged from 9 to 604 people (median 21) and included people with intellectual disability, health professionals, carers and support people, and others working with people with intellectual disability. Six themes were identified: (1) health professionals’ attitudes and lack of education, (2) inadequate accessible health information, (3) involvement of support people, (4) systemic constraints, (5) person-centred informed consent and (6) effective communication between health professionals and patients. Themes were barriers (themes 1, 2 and 4), enablers (themes 5 and 6) or both (theme 3).

Conclusions Multiple reasons contribute to poor consent practices for people with intellectual disability in current health systems. Recommendations include addressing health professionals’ attitudes and lack of education in informed consent with clinician training, the co-production of accessible information resources and further inclusive research into informed consent for people with intellectual disability.

PROSPERO registration CRD42021290548.

• Decision making
• Healthcare quality improvement
• Patient-centred care
• Quality improvement
• Standards of care

Data availability statement

Data are available upon reasonable request. Additional data and materials such as data collection forms, data extraction and analysis templates and QualSyst assessment data can be obtained by contacting the corresponding author.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/ .

https://doi.org/10.1136/bmjqs-2023-016113

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What is already known on this topic

People with intellectual disability are frequently excluded from decision-making processes and not provided equal opportunity for informed consent, despite protections outlined in the United Nations Convention on the Rights of Persons with Disabilities.

People with intellectual disability have the capacity and desire to make informed medical decisions, which can improve their well-being, health satisfaction and health outcomes.

What this review study adds

Health professionals lack adequate training in valid informed consent and making reasonable adjustments for people with intellectual disability, and continue to perpetuate assumptions of incapacity.

Health information provided to people with intellectual disability is often inaccessible and insufficient for them to make informed decisions about healthcare.

The role of support people, systemic constraints, a person-centred approach and ineffective healthcare communication also affect informed consent.

How this review might affect research, practice or policy

Health professionals need additional training on how to provide a valid informed consent process for people with intellectual disability, specifically in using accessible health information, making reasonable adjustments (e.g., longer/multiple appointments, options of a support person attending or not, using plain English), involving the individual in discussions, and communicating effectively with them.

Inclusive research is needed to hear the voices and opinions of people with intellectual disability about healthcare decision-making and about informed consent practices in specific healthcare settings.

Introduction

Approximately 1% of the world’s population have intellectual disability. 1 Intellectual disability is medically defined as a group of neurodevelopmental conditions beginning in childhood, with below average cognitive functioning and adaptive behaviour, including limitations in conceptual, social and practical skills. 2 People with intellectual disability prefer an alternative strength-based definition, reflected in the comment by Robert Strike OAM (Order of Australia Medal): ‘We can learn if the way of teaching matches how the person learns’, 3 reinforcing the importance of providing information tailored to the needs of a person with intellectual disability. A diagnosis of intellectual disability is associated with significant disparities in health outcomes. 4–7 Person-centred decision-making and better communication have been shown to improve patient satisfaction, 8 9 the physician–patient relationship 10 and overall health outcomes 11 for the wider population. Ensuring people with intellectual disability experience informed decision-making and accessible healthcare can help address the ongoing health disparities and facilitate equal access to healthcare.

Bodily autonomy is an individual’s power and agency to make decisions about their own body. 12 Informed consent for healthcare enables a person to practice bodily autonomy and is protected, for example, by the National Safety and Quality Health Service Standards (Australia), 13 Mental Capacity Act (UK) 14 and the Joint Commission Standards (USA). 15 In this article, we define informed consent according to three requirements: (1) the person is provided with information they understand, (2) the decision is free of coercion and (3) the person must have capacity. 16 For informed consent to be valid, this process must be suited to the individual’s needs so that they can understand and communicate effectively. Capacity is the ability to give informed consent for a medical intervention, 17 18 and the Mental Capacity Act outlines that ‘a person must be assumed to have capacity unless it is established that he lacks capacity’ and that incapacity can only be established if ‘all practicable steps’ to support capacity have been attempted without success. 14 These assumptions of capacity are also decision-specific, meaning an individual’s ability to consent can change depending on the situation, the choice itself and other factors. 17

Systemic issues with healthcare delivery systems have resulted in access barriers for people with intellectual disability, 19 despite the disability discrimination legislation in many countries who are signatories to the United Nations (UN) Convention on the Rights of Persons with Disabilities. 20 Patients with intellectual disability are not provided the reasonable adjustments that would enable them to give informed consent for medical procedures or interventions, 21 22 despite evidence that many people with intellectual disability have both the capacity and the desire to make their own healthcare decisions. 21 23

To support people with intellectual disability to make independent health decisions, an equitable and accessible informed consent process is needed. 24 However, current health systems have consistently failed to provide this. 21 25 To address this gap, we must first understand the factors that contribute to inequitable and inaccessible consent. To the best of our knowledge, the only current review of informed consent for people with intellectual disability is an integrative review by Goldsmith et al . 26 Many of the included articles focused on assessment of capacity 27–29 and research consent. 30–32 The review’s conclusion supported the functional approach to assess capacity, with minimal focus on how the informed consent processes can be improved. More recently, there has been a move towards ensuring that the consent process is accessible for all individuals, including elderly patients 33 and people with aphasia. 34 However, there remains a paucity of literature about the informed consent process for people with intellectual disability, with no systematic reviews summarising the factors influencing the healthcare consent process for people with intellectual disability.

To identify barriers to and enablers of the informed healthcare consent process for people with intellectual disability, and to understand how this can be made equitable and accessible.

A systematic literature review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P) systematic literature review protocol. 35 The PRISMA 2020 checklist 36 and ENhancing Transparency in REporting the synthesis of Qualitative research (ENTREQ) reporting guidelines were also followed. 37 The full study protocol is included in online supplemental appendix 1 .

Supplemental material

No patients or members of the public were involved in this research for this manuscript.

Search strategy

A search strategy was developed to identify articles about intellectual disability, consent and healthcare interventions, described in online supplemental appendix 2 . Multiple databases were searched for articles published between January 1990 to January 2022 (Embase, MEDLINE, PsychINFO, PubMed, SCOPUS, Web of Science and CINAHL). These databases include healthcare and psychology databases that best capture relevant literature on this topic, including medical, nursing, social sciences and bioethical literature. The search was limited to studies published from 1990 as understandings of consent have changed since then. 38 39 This yielded 4853 unique papers which were imported into Covidence, a specialised programme for conducting systematic reviews. 40

Study selection

Citation screening by abstract and titles was completed by two independent researchers (MD and EEP). Included articles had to:

Examine the informed consent process for a healthcare intervention for people with intellectual disability.

Have collected more than 50% of its data from relevant stakeholders, including adults with intellectual disability, families or carers of a person with intellectual disability, and professionals who engage with people with intellectual disability.

Report empirical data from primary research methodology.

Be published in a peer-reviewed journal after January 1990.

Be available in English.

Full text screening was completed by two independent researchers (MD and EEP). Articles were excluded if consent was only briefly discussed or if it focused on consent for research, capacity assessment, or participant knowledge or comprehension. Any conflicts were resolved through discussion with an independent third researcher (IS).

Additional studies were identified through an ancestral search and by hand-searching three major journals relevant to intellectual disability research. Journals were selected if they had published more than one included article for this review or in previous literature reviews conducted by the research team.

Quality assessment

Two independent researchers (MD and IS) assessed study quality with the QualSyst tool, 41 which can assess both qualitative and quantitative research papers. After evaluating the distribution of scores, a threshold value of 55% was used, as suggested by QualSyst 41 to exclude poor-quality studies but capture enough studies overall. Any conflicts between the quality assessment scores were resolved by a third researcher (EEP). For mixed-method studies, both qualitative and quantitative quality scores were calculated, and the higher value used.

Data collection

Two independent researchers (MD and JH) reviewed each study and extracted relevant details, including study size, participant demographics, year, country of publication, study design, data analysis and major outcomes reported. Researchers used standardised data collection forms designed, with input from senior researchers with expertise in qualitative research (IS and EEP), to extract data relevant to the review’s research aims. The form was piloted on one study, and a second iteration made based on feedback. These forms captured data on study design, methods, participants, any factors affecting the process of informed consent and study limitations. Data included descriptions and paragraphs outlining key findings, the healthcare context, verbatim participant quotes and any quantitative analyses or statistics. Missing or unclear data were noted.

Data analysis

A pilot literature search showed significant heterogeneity in methodology of studies, limiting the applicability of traditional quantitative analysis (ie, meta-analysis). Instead, inductive thematic analysis was chosen as an alternative methodology 42 43 that has been used in recent systematic reviews examining barriers and enablers of other health processes. 44 45 The six-phase approach described by Braun and Clarke was used. 46 47 A researcher (MD) independently coded the extracted data of each study line-by-line, with subsequent data grouped into pre-existing codes or new concepts when necessary. Codes were reviewed iteratively and grouped into categories, subthemes and themes framed around the research question. Another independent researcher (JH) collated and analysed the data on study demographics, methods and limitations. The themes were reviewed by two senior researchers (EEP and IS).

Qualitative methods of effect size calculations have been described in the literature, 48 49 which was captured in this review by the number of studies that identified each subtheme, with an assigned frequency rating to compare their relative significance. Subthemes were given a frequency rating of A, B, C or D if they were identified by >10, 7–9, 4–6 or <3 articles, respectively. The overall significance of each theme was estimated by the number of studies that mentioned it and the GRADE framework, a stepwise approach to quality assessment using a four-tier rating system. Each study was evaluated for risk of bias, inconsistency, indirectness, imprecision and publication bias. 50 51 Study sensitivity was assessed by counting the number of distinct subthemes included. 52 The quality of findings was designated high, moderate or low depending on the frequency ratings, the QualSyst score and the GRADE scores of studies supporting the finding. Finally, the relative contributions of each study were evaluated by the number of subthemes described, guided by previously reported methods for qualitative reviews. 52

Co-research

The findings were reviewed by two co-researchers with intellectual disability (JL and SS), with over 30 years combined experience as members and employees of a self-advocacy organisation. Guidance on the findings and an easy read summary was produced in line with best-practice inclusive research 53 54 over multiple discussions. Input from two health professional researchers (MD and EEP) provided data triangulation and sense-checking of findings.

Twenty-three articles were identified ( figure 1 ): 14 qualitative, 6 quantitative and 3 mixed-methods. Two papers included the same population of study participants: McCarthy 55 and McCarthy, 56 but had different research questions. Fovargue et al 57 was excluded due to a quality score of 35%. Common quality limitations were a lack of verification procedures to establish credibility and limited researcher reflexivity. No studies were excluded due to language requirements (as all were in English) or age restrictions (all studies had majority adult participants).

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PRISMA 2020 flowchart for the systematic review. 36

Studies were published from 1999 to 2020 and involved participant populations from the UK (n=18), USA (n=3), Sweden (n=1) and Ireland (n=1). Participant numbers ranged from 9 to 604 (median 21), and participants included people with intellectual disability (n=817), health professionals (n=272), carers and support people (n=48), and other professionals that work with people with intellectual disability (n=137, community service agency directors, social workers, administrative staff and care home staff). Ages of participants ranged from 8 to 84 years, though only Aman et al 58 included participants <18 years of age. This study was included as the article states very few children were included. Studies examined consent in different contexts, including contraception and sexual health (6/23 articles), 58–60 medications (5/23 articles), 58–62 emergency healthcare, 63 cervical screening, 64 community referrals, 58–61 65 mental health, 66 hydrotherapy, 64 blood collection 67 and broad decision-making consent without a specific context. 65 68–71 A detailed breakdown of each study is included in online supplemental appendix 3 .

Six major themes were identified from the studies, summarised in figure 2 . An overview of included studies showing study sensitivity, effect size, QualSyst and GRADE scores is given in online supplemental appendix 4 . Studies with higher QualSyst and GRADE scores contributed more to this review’s findings and tended to include more subthemes; specifically, Rogers et al , 66 Sowney and Barr, 63 Höglund and Larsson, 72 and McCarthy 55 and McCarthy. 56 Figure 3 gives the easy read version of theme 1, with the full easy read summary in online supplemental appendix 5 .

Summary of the identified six themes and subthemes.

Theme 1 of the easy read summary.

Theme 1—Health professionals’ attitudes and lack of education about informed consent

Health professionals’ attitudes and practices were frequently (18/21) identified as factors affecting the informed consent process, with substantial evidence supporting this theme. Studies noted the lack of training for health professionals in supporting informed consent for people with intellectual disability, their desire for further education, and stereotypes and discrimination perpetuated by health professionals.

Lack of health professional education on informed consent and disability discrimination legislation

Multiple studies reported inconsistent informed consent practices, for various reasons: some reported that health professionals ‘forgot’ to or ‘did not realise consent was necessary’, 63 73 but inconsistent consent practices were also attributed to healthcare providers’ unfamiliarity with consent guidelines and poor education on this topic. Carlson et al 73 reported that only 44% of general practitioners (GPs) were aware of consent guidelines, and there was the misconception that consent was unnecessary for people with intellectual disability. Similarly, studies of psychologists 66 and nurses 63 found that many were unfamiliar with their obligations to obtain consent, despite the existence of anti-discrimination legislation. People with intellectual disability describe feeling discriminated against by health professionals, reflected in comments such as ‘I can tell, my doctor just thinks I’m stupid – I'm nothing to him’. 74 Poor consent practices by health professionals were observed in Goldsmith et al , 67 while health professionals surveyed by McCarthy 56 were unaware of their responsibility to provide accessible health information to women with intellectual disability. Improving health professional education and training was suggested by multiple studies as a way to remove this barrier. 63 65–67 69 73

Lack of training on best practices for health professions caring for people with intellectual disability

A lack of training in caring for and communicating with people with intellectual disability was also described by midwives, 72 psychologists, 66 nurses, 63 pharmacists 61 and GPs. 56 72 75 Health professionals lacked knowledge about best practice approaches to providing equitable healthcare consent processes through reasonable adjustments such as accessible health information, 56 60 66 longer appointments times, 60 72 simple English 62 67 and flexible approaches to patient needs. 63 72

Health professionals’ stereotyping and assumptions of incapacity

Underlying stereotypes contributed to some health professionals’ (including nurses, 63 GPs 56 and physiotherapists 64 ) belief that people with intellectual disability lack capacity and therefore, do not require opportunities for informed consent. 56 64 In a survey of professionals referring people with intellectual disability to a disability service, the second most common reason for not obtaining consent was ‘patient unable to understand’. 73

Proxy consent as an inappropriate alternative

People with intellectual disability are rarely the final decision-maker in their medical choices, with many health providers seeking proxy consent from carers, support workers and family members, despite its legal invalidity. In McCarthy’s study (2010), 18/23 women with intellectual disability said the decision to start contraception was made by someone else. Many GPs appeared unaware that proxy consent is invalid in the UK. 56 Similar reports came from people with intellectual disability, 55 56 60 64 69 76 health professionals (nurses, doctors, allied health, psychologists), 56 63 64 66 77 support people 64 77 and non-medical professionals, 65 73 and capacity was rarely documented. 56 62 77

Exclusion of people with intellectual disability from decision-making discussions

Studies described instances where health professionals made decisions for their patients with intellectual disability or coerced patients into a choice. 55 72 74 76 77 In Ledger et al 77 , only 62% of women with intellectual disability were involved in the discussion about contraception, and only 38% made the final decision, and others stated in Wiseman and Ferrie 74 : ‘I was not given the opportunity to explore the different options. I was told what one I should take’. Three papers outlined instances where the choices of people with intellectual disability were ignored despite possessing capacity 65 66 69 and when a procedure continued despite them withdrawing consent. 69

Theme 2—Inadequate accessible health information

Lack of accessible health information.

The lack of accessible health information was the most frequently identified subtheme (16/23 studies). Some studies reported that health professionals provided information to carers instead, 60 avoided providing easy read information due to concerns about ‘offending’ patients 75 or only provided verbal information. 56 67 Informed consent was supported when health professionals recognised the importance of providing medical information 64 and when it was provided in an accessible format. 60 Alternative approaches to health information were explored, including virtual reality 68 and in-person education sessions, 59 with varying results. Overall, the need to provide information in different formats tailored to an individual’s communication needs, rather than a ‘one size fits all’ approach, was emphasised by both people with intellectual disability 60 and health professionals. 66

Insufficient information provided

Studies described situations where insufficient information was provided to people with intellectual disability to make informed decisions. For example, some people felt the information from their GP was often too basic to be helpful (Fish et al 60 ) and wanted additional information on consent forms (Rose et al 78 ).

Theme 3—The involvement of support people

Support people (including carers, family members and group home staff) were identified in 11 articles as both enablers of and barriers to informed consent. The antagonistic nature of these findings and lower frequency of subthemes are reflected in the lower quality assessments of evidence.

Support people facilitated communication with health professionals

Some studies reported carers bridging communication barriers with health to support informed consent. 63 64 McCarthy 56 found 21/23 of women with intellectual disability preferred to see doctors with a support person due to perceived benefits: ‘Sometimes I don’t understand it, so they have to explain it to my carer, so they can explain it to me easier’. Most GPs in this study (93%) also agreed that support people aided communication.

Support people helped people with intellectual disability make decisions

By advocating for people with intellectual disability, carers encouraged decision-making, 64 74 provided health information, 74 77 emotional support 76 and assisted with reading or remembering health information. 55 58 76 Some people with intellectual disability explicitly appreciated their support person’s involvement, 60 such as in McCarthy’s 55 study where 18/23 participants felt supported and safer when a support person was involved.

Support people impeded individual autonomy

The study by Wiseman and Ferrie 74 found that while younger participants with intellectual disability felt family members empowered their decision-making, older women felt family members impaired their ability to give informed consent. This was reflected in interviews with carers who questioned the capacity of the person with intellectual disability they supported and stated they would guide them to pick the ‘best choice’ or even over-ride their choices. 64 Studies of psychologists and community service directors described instances where the decision of family or carers was prioritised over the wishes of the person with intellectual disability. 65 66 Some women with intellectual disability in McCarthy’s studies (2010, 2009) 55 56 appeared to have been coerced into using contraception by parental pressures or fear of losing group home support.

Theme 4—Systemic constraints within healthcare systems

Time restraints affect informed consent and accessible healthcare.

Resource limitations create time constraints that impair the consent process and have been identified as a barrier by psychologists, 66 GPs, 56 hospital nurses 63 and community disability workers. 73 Rogers et al 66 highlighted that a personalised approach that could improve informed decision-making is restricted by inflexible medical models. Only two studies described flexible patient-centred approaches to consent. 60 72 A survey of primary care practices in 2007 reported that most did not modify their cervical screening information for patients with intellectual disability because it was not practical. 75

Inflexible models of consent

Both people with intellectual disability 76 and health professionals 66 recognised that consent is traditionally obtained through one-off interactions prior to an intervention. Yet, for people with intellectual disability, consent should ideally be an ongoing process that begins before an appointment and continues between subsequent ones. Other studies have tended to describe one-off interactions where decision-making was not revisited at subsequent appointments. 56 60 72 76

Lack of systemic supports

In one survey, self-advocates highlighted a lack of information on medication for people with intellectual disability and suggested a telephone helpline and a centralised source of information to support consent. 60 Health professionals also want greater systemic support, such as a health professional specialised in intellectual disability care to support other staff, 72 or a pharmacist specifically to help patients with intellectual disability. 61 Studies highlighted a lack of guidelines about healthcare needs of people with intellectual disabilities such as contraceptive counselling 72 or primary care. 75

Theme 5—Person-centred informed consent

Ten studies identified factors related to a person-centred approach to informed consent, grouped below into three subthemes. Health professionals should tailor their practice when obtaining informed consent from people with intellectual disability by considering how these subthemes relate to the individual. Each subtheme was described five times in the literature with a relative frequency rating of ‘C’, contributing to overall lower quality scores.

Previous experience with decision-making

Arscott et al 71 found that the ability of people with intellectual disability to consent changed with their verbal and memory skills and in different clinical vignettes, supporting the view of ‘functional’ capacity specific to the context of the medical decision. Although previous experiences with decision-making did not influence informed consent in this paper, other studies suggest that people with intellectual disability accustomed to independent decision-making were more able to make informed medical decisions, 66 70 and those who live independently were more likely to make independent healthcare decisions. 56 Health professionals should be aware that their patients with intellectual disability will have variable experience with decision-making and provide individualised support to meet their needs.

Variable awareness about healthcare rights

Consent processes should be tailored to the health literacy of patients, including emphasising available choices and the option to refuse treatment. In some studies, medical decisions were not presented to people with intellectual disability as a choice, 64 and people with intellectual disability were not informed of their legal right to accessible health information. 56

Power differences and acquiescence

Acquiescence by people with intellectual disability due to common and repeated experiences of trauma—that is, their tendency to agree with suggestions made by carers and health professionals, often to avoid upsetting others—was identified as an ongoing barrier. In McCarthy’s (2009) interviews with women with intellectual disability, some participants implicitly rejected the idea that they might make their own healthcare decisions: ‘They’re the carers, they have responsibility for me’. Others appeared to have made decisions to appease their carers: ‘I have the jab (contraceptive injection) so I can’t be blamed for getting pregnant’. 55 Two studies highlighted that health professionals need to be mindful of power imbalances when discussing consent with people with intellectual disability to ensure the choices are truly autonomous. 61 66

Theme 6—Effective communication between health professionals and patients

Implementation of reasonable adjustments for verbal and written information.

Simple language was always preferred by people with intellectual disability. 60 67 Other communication aids used in decision-making included repetition, short sentences, models, pictures and easy read brochures. 72 Another reasonable adjustment is providing the opportunity to ask questions, which women with intellectual disability in McCarthy’s (2009) study reported did not occur. 55

Tailored communication methods including non-verbal communication

Midwives noted that continuity of care allows them to develop rapport and understand the communication preferences of people with intellectual disability. 72 This is not always possible; for emergency nurses, the lack of background information about patients with intellectual disability made it challenging to understand their communication preferences. 63 The use of non-verbal communication, such as body language, was noted as underutilised 62 66 and people with intellectual disability supported the use of hearing loops, braille and sign language. 60

To the best of our knowledge, this is the first systematic review investigating the barriers and enablers of the informed consent process for healthcare procedures for people with intellectual disability. The integrative review by Goldsmith et al 26 examined capacity assessment and shares only three articles with this systematic review. 69 71 73 Since the 2000s, there has been a paradigm shift in which capacity is no longer considered a fixed ability that only some individuals possess 38 39 but instead as ‘functional’: a flexible ability that changes over time and in different contexts, 79 reflected in Goldsmith’s review. An individual’s capacity can be supported through various measures, including how information is communicated and how the decision-making process is approached. 18 80 By recognising the barriers and enablers identified in this review, physicians can help ensure the consent process for their patients with intellectual disability is both valid and truly informed. This review has highlighted the problems of inaccessible health information, insufficient clinical education on how to make reasonable adjustments and lack of person-centred trauma-informed care.

Recommendations

Health professionals require training in the informed consent process for people with intellectual disability, particularly in effective and respectful communication, reasonable adjustments and trauma-informed care. Reasonable adjustments include offering longer or multiple appointments, using accessible resources (such as easy read information or shared decision-making tools) and allowing patient choices (such as to record a consultation or involve a support person). Co-researchers reported that many people with intellectual disability prefer to go without a support person because they find it difficult to challenge their decisions and feel ignored if the health professional only talks to the support person. People with intellectual disability also feel they cannot seek second opinions before making medical decisions or feel pressured to provide consent, raising the possibility of coercion. These experiences contribute to healthcare trauma. Co-researchers raised the importance of building rapport with the person with intellectual disability and of making reasonable adjustments, such as actively advocating for the person’s autonomy, clearly stating all options including the choice to refuse treatment, providing opportunities to contribute to discussions and multiple appointments to ask questions and understand information. They felt that without these efforts to support consent, health professionals can reinforce traumatic healthcare experiences for people with intellectual disability. Co-researchers noted instances where choices were made by doctors without discussion and where they were only given a choice after requesting one and expressed concern that these barriers are greater for those with higher support needs.

Co-researchers showed how these experiences contributed to mistrust of health professionals and poorer health outcomes. In one situation, a co-researcher was not informed of a medication’s withdrawal effects, resulting in significant side-effects when it was ceased. Many people with intellectual disability describe a poor relationship with their health professionals, finding it difficult to trust health information provided due to previous traumatic experiences of disrespect, coercion, lack of choice and inadequate support. Many feel they cannot speak up due to the power imbalance and fear of retaliation. Poor consent practices and lack of reasonable adjustments directly harm therapeutic alliances by reducing trust, contribute to healthcare trauma and lead to poorer health outcomes for people with intellectual disability.

Additional education and training for health professionals is urgently needed in the areas of informed consent, reasonable adjustments and effective communication with people with intellectual disability. The experiences of health professionals within the research team confirmed that there is limited training in providing high-quality healthcare for people with intellectual disability, including reasonable adjustments and accessible health information. Co-researchers also suggested that education should be provided to carers and support people to help them better advocate for people with intellectual disability.

Health information should be provided in a multimodal format, including written easy read information. Many countries have regulation protecting the right to accessible health information and communication support to make an informed choice, such as UK’s Accessible Information Standard, 81 and Australia’s Charter of Health Care Rights, 24 yet these are rarely observed. Steps to facilitate this include routinely asking patients about information requirements, system alerts for an individual’s needs or routinely providing reasonable adjustments. 82 Co-researchers agreed that there is a lack of accessible health information, particularly about medications, and that diagrams and illustrations are underutilised. There is a critical need for more inclusive and accessible resources to help health professionals support informed consent in a safe and high-quality health system. These resources should be created through methods of inclusive research, such as co-production, actively involving people with intellectual disability in the planning, creation, and feedback process. 53

Strengths and limitations

This systematic review involved two co-researchers with intellectual disability in sense-checking findings and co-creating the easy read summary. Two co-authors who are health professionals provided additional sense-checking of findings from a different stakeholder perspective. In future research, this could be extended by involving people with intellectual disability in the design and planning of the study as per recommendations for best-practice inclusive research. 53 83

The current literature is limited by low use of inclusive research practices in research involving people with intellectual disability, increasing vulnerability to external biases (eg, inaccessible questionnaires, involvement of carers in data collection, overcompliance or acquiescence and absence of researcher reflexivity). Advisory groups or co-research with people with intellectual disability were only used in five studies. 58 60 68 74 76 Other limitations include unclear selection criteria, low sample sizes, missing data, using gatekeepers in patient selection and predominance of UK-based studies—increasing the risk of bias and reducing transferability. Nine studies (out of 15 involving people with intellectual disability) explicitly excluded those with severe or profound intellectual disability, reflecting a selection bias; only one study specifically focused on people with intellectual disability with higher support needs. Studies were limited to a few healthcare contexts, with a focus on consent about sexual health, contraception and medications.

The heterogeneity and qualitative nature of studies made it challenging to apply traditional meta-analysis. However, to promote consistency in qualitative research, the PRISMA and ENTREQ guidelines were followed. 36 37 Although no meta-analyses occurred, the duplication of study populations in McCarthy 2009 and 2010 likely contributed to increased significance of findings reported in both studies. Most included studies (13/23) were published over 10 years ago, reducing the current relevance of this review’s findings. Nonetheless, the major findings reflect underlying systemic issues within the health system, which are unlikely to have been resolved since the articles were published, as the just-released final report of the Australian Royal Commission into Violence, Abuse, Neglect and Exploitation of People with Disability highlights. 84 There is an urgent need for more inclusive studies to explore the recommendations and preferences of people with intellectual disability about healthcare choices.

Informed consent processes for people with intellectual disability should include accessible information and reasonable adjustments, be tailored to individuals’ needs and comply with consent and disability legislation. Resources, guidelines and healthcare education are needed and should cover how to involve carers and support people, address systemic healthcare problems, promote a person-centred approach and ensure effective communication. These resources and future research must use principles of inclusive co-production—involving people with intellectual disability at all stages. Additionally, research is needed on people with higher support needs and in specific contexts where informed consent is vital but under-researched, such as cancer screening, palliative care, prenatal and newborn screening, surgical procedures, genetic medicine and advanced therapeutics such as gene-based therapies.

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Supplementary materials

Supplementary data.

This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.

• Data supplement 1
• Data supplement 2
• Data supplement 3
• Data supplement 4
• Data supplement 5

Contributors MD, EEP and IS conceived the idea for the systematic review. MD drafted the search strategy which was refined by EEP and IS. MD and EEP completed article screening. MD and IS completed quality assessments of included articles. MD and JH completed data extraction. MD drafted the original manuscript. JL and SS were co-researchers who sense-checked findings and were consulted to formulate dissemination plans. JL and SS co-produced the easy read summary with MD, CM, JH, EEP and IS. MD, JLS, EEP and IS reviewed manuscript wording. All authors critically reviewed the manuscript and approved it for publication. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted. MD is the guarantor responsible for the overall content of this manuscript.

Funding This systematic literature review was funded by the National Health & Medical Research Council (NHMRC), Targeted Call for Research (TCR) into Improving health of people with intellectual disability. Research grant title "GeneEQUAL: equitable and accessible genomic healthcare for people with intellectual disability". NHMRC application ID: 2022/GNT2015753.

Competing interests None declared.

Provenance and peer review Not commissioned; externally peer reviewed.

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

Linked Articles

• Editorial It is up to healthcare professionals to talk to us in a way that we can understand: informed consent processes in people with an intellectual disability Jonathon Ding Richard Keagan-Bull Irene Tuffrey-Wijne BMJ Quality & Safety 2024; 33 277-279 Published Online First: 30 Jan 2024. doi: 10.1136/bmjqs-2023-016830

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