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TSH Levels: Normal, High, or Low (Including Optimal Thyroid Levels)

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TSH is a hormone secreted by the brain’s pituitary gland to control the activity of your thyroid gland. TSH stands for thyroid stimulating hormone and as its name suggests, it stimulates the thyroid to produce thyroid hormones. Levels of TSH affect the production the hormones triiodothyronine (T3) and thyroxine (T4). Doctors usually test TSH level to see if it’s within the normal range if you show symptoms of an overactive or underactive thyroid.

You may also have to regularly go for a TSH blood test or T4 blood test if you are receiving hormone treatment for a thyroid condition.

Optimal TSH levels are critical for your body’s function, including your general health and wellbeing. Thyroid hormones help control your metabolic rate, heart function, nervous system, and digestion. Although TSH isn’t classed as a thyroid hormone, high or low TSH levels can disrupt levels of T3 and T4. This can result in symptoms of hyperthyroidism or hypothyroidism.

In this article, you will find out all you need to know about TSH and how it affects your thyroid hormone levels. You will also learn about thyroid-related symptoms if TSH levels are higher or lower than the normal range.

What Does the Thyroid Do?

Your thyroid gland is a small butterfly-shaped organ that sits in the front part of your neck just above the middle of your collarbone. PubMed Health says that your thyroid continually secretes hormones into your bloodstream. Usually, more thyroid hormones are produced when the body needs more energy, like when it is growing or during pregnancy. 1

What is TSH (Thyroid-Stimulating Hormone)?

The hypothalamus, in the base of the brain, releases TRH (thyrotropin-releasing hormone) to stimulate the pituitary gland. The pituitary gland then produce TSH to stimulate production of thyroid hormones (T4 and T3) that affect almost every organ in your body.

In optimal conditions, TSH levels ensure that just enough T3 and T4 hormones are released into your bloodstream.

Dr. Neha Pathak on WebMD says that thyroid stimulating hormone (TSH) is produced by the pituitary gland in your brain. The reasons that TSH levels can fluctuate is mainly due to levels of T3 or T4 in your blood. 2

High TSH levels can mean that your thyroid is sluggish and underactive because there is not enough T3 or T4 being produced. If you are pregnant, it’s normal for TSH levels to become slightly elevated. 2

Low TSH levels can indicate an overactive thyroid condition and can be a result of an autoimmune condition or having too much iodine in your diet. 2

The chart below helps you see how TSH controls the thyroid.

Thyroid System (TRH, TSH, T3, T4)

Dr. Oliver Starr on Patient.info explains more about what TSH is. Dr. Starr says that the pituitary gland in your brain should produce the right amount of TSH. This, in turn, stimulates the thyroid to produce the right amount of thyroxine (T4) and triiodothyronine (T3). 7

The information on the levels of thyroid hormones in your blood is then fed back to your brain. This is called the feedback loop. As T4 and T3 levels in the blood rise, feedback to your brain tells it to produce less TSH. However, if thyroid hormones levels are too low, your pituitary gland will produce more thyroid stimulating hormone to increase thyroid hormone levels.

T3 and T4: What Are They?

Triiodothyronine (T3) and thyroxine (T4) are two thyroid hormones that TSH stimulates.

Doctors say that T4 is the most important of the thyroid hormones and affects almost every function in the human body. 3 If doctors suspect hyperthyroidism or hypothyroidism, they usually test T4 levels. T3 is the most powerful thyroid hormone, and as T4 it affects almost every process in the body. 4

T3 and T4 hormones usually bind themselves to proteins in the blood where they are delivered to your cells. Some hormone, however, doesn’t attach to protein and this is called free T4 or free T3. Doctors will usually test for free T4 (FT4) to see how much of the hormone is available for your body’s energy requirements.

Related article: What are T3 and T4: The Complete Guide to Your Thyroid Hormones

Normal Range for T3 and T4

If your TSH levels are abnormally high or low, doctors will usually arrange for free T4 or free T3 blood test. These tests can help doctors diagnose if you suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (under active thyroid).

Free T4 (T4) range

Dr. Muhammad Bader Hammami on Medscape says that free T4 (FT4) range is as follows: 5

• Children and adolescents : 0.8 – 2 ng/dL (10 – 26 pmol/L)
• Adults : 0.7 – 1.8 ng/dL (9 – 23 pmol/L)
• Pregnant women : 0.5 – 1 ng/dL (6.5 – 13 pmol/L)

The total thyroxine (TT4) range is as follows:

• Babies up to 2 weeks old : 11.8 – 22.6 mcg/dL (152-292 nmol/L)
• Infants over 2 weeks old and children : 6.4 – 13.3 mcg/dL (83 – 172 nmol/L)
• Adults : 5.4 – 11.5 mcg/dL (57 – 148 nmol/L)

Free T3 (T3)

According to Dr. Jayita Poduval on Medscape, only adults are usually tested for levels of free T3. Test results are measured in picograms per deciliter. The normal free T3 (FT3) range is as follows: 6

• Adults : 260 – 480 pg/dL (4 – 7.4 pmol/L)

The normal reference range of triiodothyronine (TT3) is as follows:

• Children : 125 – 250 ng/dL
• Adults : 80 – 220 ng/dL

Normal TSH Levels (Normal Thyroid Levels)

A thyroid function test usually starts with testing if TSH levels are normal and if free T4 levels are within the normal range. According to Dr. Oliver Starr (quoted earlier), normal thyroid levels depend on a few things like your age, if you are pregnant or not, or taking certain medications. 7

Dr. Starr recommends testing TSH levels under a doctor’s supervision rather than doing a hypothyroidism test at home.

TSH normal range

According to the U.S. National Library of Medicine the normal TSH range in healthy adults is 0.4 to 4.0 milli-international units per liter (0.4 – 4.0 mIU/L). 7

For your thyroid to be working correctly, your lab test results for normal free T4 levels should be 9 – 23 pmol/L (0.7 – 1.8 ng/dL)

However, recent studies into optimal thyroid levels have recommended that the upper normal range for TSH hormone tests should be lowered. According to the Journal of Clinical Endocrinology & Metabolism , an upper limit of 2.5 mIU/L is more appropriate as the currently accepted TSH normal range. 8

This is because individuals with TSH in the range of 2.5 – 4.0 mIU/L are considered to be in the risk group for developing thyroid disorders.

However, it is accepted that the normal TSH range increases with age.

Let’s look in more detail at the normal levels of TSH that are age-specific or take into account pregnancy.

TSH levels for premature birth

Babies born prematurely often suffer from thyroid dysfunction, and all babies have their thyroid levels routinely tested. According to microbiologist Dr. Alina G. Sofronescu, the TSH levels for premature birth are: 9

• Premature infants : 0.7 – 27.0 mIU/L

TSH levels for children

The Journal of Clinical Endocrinology & Metabolism says that the normal TSH range for children that take into account their age is as follows:

• Infants 1 day old : 1.9 – 17.58 mIU/L
• Infants 1 week old : 0.58 – 5.57 mIU/L
• Children one-year-old : 0.57 – 5.54 mIU/L
• Adolescents 18 years old : 0.51 – 4.93 mIU/L

TSH levels for adults (men and women)

The normal TSH range for adult men and women is as follows:

• Adults aged 21-54 : 0.4 – 4.0 mIU/L

Depending on the lab, some doctors give the normal TSH level as 0.4 – 4.2 mIU/L.

TSH levels during pregnancy

Thyroid-stimulating hormone can fluctuate during pregnancy due to the baby’s growth and extra stress on the thyroid.

According to doctors from Medscape, the normal TSH range during the 3 trimesters of pregnancy are as follows: 9

• First trimester : 0.3 – 4.5 mIU/L
• Second trimester : 0.5 – 4.6 mIU/L
• Third trimester : 0.8 – 5.2 mIU/L

However, a study published in 2015 recommended that cut off points for TSH levels during pregnancy should be lowered. The journal Clinical Chemistry stated that high TSH levels during the first trimester should be viewed as anything over 2.5 mU/L. During the second and third trimester, the TSH normal range for pregnant women should be 0.2 – 3.0 mU/L. 11

TSH Normal Range by Age

In older adults, it is expected that normal levels of TSH increases. The Journal of Clinical Endocrinology & Metabolism published a report specifying age-specific TSH ranges for older adults. These are as follows: 15

• Adults aged 51 – 60 : 0.51 – 4.36 mU/L
• Adults aged 61 – 70 : 0.48 – 4.59 mU/L
• Adults aged 71 – 80 : 0.40 – 4.96 mU/L
• Adults over 80 : 0.36 – 5.94 mU/L

High TSH Levels

Generally, high TSH levels are an indication of an underactive thyroid or hypothyroidism.

Doctors from the Mayo Clinic say that blood tests for hypothyroidism usually show elevated TSH and low thyroxine (T4) levels. Subsequent blood tests will help to determine the best medication for treating hypothyroidism and the right dosage. 12

Dr. Ruchi Mathur who specializes in endocrinology and metabolic disorders says that some people have subclinical hypothyroidism. This is where thyroid function tests show high TSH but normal T4 and T3. Usually, there are no obvious symptoms of subclinical hypothyroidism. 13

Symptoms of elevated TSH levels

Your doctor will usually have you take a blood test for hypothyroidism if you are showing symptoms of too little thyroid hormones but high TSH. Dr. Ruchi Mathur says that some symptoms of hypothyroidism include: 13

• Increased sensitivity to cold
• Weight gain and difficulty losing weight
• Dry skin and hair
• Wanting to sleep all the time
• Tenderness and stiffness in your joints and muscles
• Mood changes like depression

Low TSH Levels

TSH level below 0.4 mU/L is considered low.

Your pituitary gland may not produce enough TSH if your thyroid is secreting more than normal thyroid hormone. Low TSH levels and high T4 and T3 levels usually are a sign of an overactive thyroid (hyperthyroidism).

Some reasons for your thyroid working overtime can include Grave’s disease (antibodies in the blood that stimulate the thyroid), goiter, or toxic adenoma (hot nodule). 14

Symptoms of lower than normal TSH levels

Dr. Oliver Starr on Patient.info says that if your pituitary gland is not producing enough TSH because of an overactive thyroid, you may experience any of the following hyperthyroidism symptoms: 15

• Restlessness with nervous behavior
• Trouble getting to sleep and disrupted sleep patterns
• Increased sweating, shortness of breath, and faster heartbeat
• Infrequent or light periods
• Visibly enlarged thyroid gland in the front of your neck

Thyroid Levels Chart (TSH Levels Chart)

Below is a TSH levels chart so that you can easily see what the normal thyroid levels are. The chart helps to show TSH, T3, and T4 levels and what you should expect to see on your lab test results.

Optimal Thyroid Levels (Optimal TSH Levels)

It can be challenging for doctors to know the optimal thyroid levels for each patient because a number of factors need to be taken into consideration.

For example, as research on treating hypothyroidism has shown, not all doctors agree on what should be classed as “normal” or high TSH levels. The traditional approach to interpreting hypothyroidism test results was to have a cutoff point at around 4.0 or 4.5 mU/L. However, some doctors challenge this and say that the normal TSH level shouldn’t be above 2.5 mU/L.

As Dr. Bernadette Biondi, who published findings on the normal TSH reference range, stated, lowering the range to 0.4 – 2.5 mU/L may end up putting more people on medication for hypothyroidism. 8

When aiming to find optimal thyroid levels when treating hypothyroidism, a doctor’s goal is to see improvement in the patient’s symptoms. This could mean that an individual’s optimal thyroid level may need to be closer to the lower end of the TSH “normal” range rather than being in the middle.

There are other factors that should be taken into consideration when determining optimal TSH levels. Let’s look at the effect age, diabetes, and heart conditions are associated with a thyroid disorder.

As we get older, our pituitary gland increase TSH hormone secretion and therefore optimal TSH range for an older may be higher than a younger person.

For example, a study in 2013 into age-related TSH ranges found that the majority of people, males and females, under 40 were well below the newly recommended threshold of 2.5 mU/L. However, after age 40, there is a significant increase in average TSH levels. The researchers concluded: “Our analysis shows that the median and range of TSH increases with age.” 8

Diabetes can also increase the amount of thyroid stimulating hormone (TSH) that controls the thyroid gland. Researchers have discovered that generally, people with diabetes have a higher concentration of TSH in blood tests. 8

According to the Journal of Diabetes Research , insulin resistance also affects thyroid function. Some studies show that many diabetics have high TSH and low thyroid hormone levels causing hypothyroidism. However, hyperthyroidism is also a risk factor for people with diabetes. 17

Heart conditions

Another issue facing doctors when finding the optimal thyroid levels is how thyroid function affects the heart.

The journal Circulation reported that thyroid hormone raises metabolic heart rate and impacts on the heart and blood pressure. For example, widened pulse pressure , hypertension, and pulmonary hypertension are some cardio-related effects of thyroid dysfunction. 18

TSH Test – Problems and Issues

One of the problems of just relying on the TSH test to check for signs of thyroid dysfunction is that it doesn’t provide a complete picture of thyroid levels.

First of all, as I’ve already pointed out, there is no consensus of opinion on what counts as high TSH levels. Most doctors stick to the traditional reference range of 4.5 mU/L, however recent studies advise the normal TSH range to be lowered to 2.5 mU/L.

Also, the journal Best Practice & Research, Clinical Endocrinology & Metabolism reported that relying on TSH tests to test thyroid function can lead to misdiagnosis. In worst-case scenarios, doctors may even fail to spot serious thyroid conditions by relying just on TSH levels. This is because sometimes TSH levels may be within the “normal” range but free T4 or free T3 levels may be higher or lower than acceptable levels. 19

Many clinics now offer combined screening for TSH levels along with checking levels of thyroxine (T4). So, if you still feel unwell and your TSH levels are not abnormal, ask your doctor to perform tests for free T4 and T3.

Other Tests for Checking the Thyroid Health

There are additional tests that check the health of your thyroid that provide more results than just TSH levels in blood serum.

The National Institute of Diabetes and Digestive and Kidney Diseases says that tests to diagnose reasons for thyroid dysfunction include: 20

• TSH testing
• Free T4 for hypothyroidism or hyperthyroidism
• Testing thyroid antibodies for Hashimoto’s disease or Grave’s disease
• Ultrasound to examine thyroid nodules
• Radioactive iodine uptake test in cases of hyperthyroidism

Read these related articles:

• How to Test Your Thyroid With a Thermometer
• Top 13 Signs That You May Have a Thyroid Disorder
• 1 Minute At Home Thyroid Cancer Self-Test: This Can Save Your Life

Medical Sources:

• NCBI . How does the thyroid work?
• WebMD . What is a TSH test?
• MedicineNet . Medical definition of thyroxine.
• MedicineNet . Medical definition of triiodothyronine.
• Medscape . Thyroxine.
• Medscape . Triiodothyronine.
• U.S. National Library of Medicine . Thyroid function tests.
• J Clin Endocrinol Metabol . 2013 Sept;98(9): 3584-3587.
• Medscape . Thyroid-stimulating hormone.
• J Clin Endocrinol Metabol . 2012 Sept;97(9): 3170-3178.
• Clin Chem . 2015 May;61(5) 704-713.
• MayoClinic . Hypothyroidism.
• MedicineNet . Hypothyroid symptoms.
• eMedicineHealth . Hyperthyroidism.
• J Clin Endocrinol Metabol . 2013 Mar;98(3): 1147-1153.
• PatientInfo . Overactive thyroid gland.
• J Diabetes Res . 2013; 2013: 390534.
• Circulation . 2007;116: 1725-1735.
• Best Pract Res Clin Endocrinol Metab . 2013 Dec; 27(6): 745–762.
• NIDDK . Thyroid tests.

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Is your Free T4 really in the Normal Range? Optimal vs Normal levels & More

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Chances are VERY high that your Free T4 level isn’t actually normal even though it may be in the “normal range”.

Most people tend to blow off their Free T4 level because it isn’t the ‘free and active’ hormone, especially when compared to free T3. 

But that is a big mistake!

Free T4 still has a story to tell and it’s not something you want to miss out on.

For instance, your Free T4 level can actually help you determine how efficient your thyroid is converting T4 into T3 and may explain why you have a “low” TSH when you still feel terrible . 

In this article, I’m going to help you understand what your Free T4 level means and teach you how to determine if it is really in the “normal range”…

Is your Free T4 Normal & Optimal?

Unfortunately, it isn’t quite that easy…

There is no magic number that your Free T4 level needs to be in order for you to suddenly start feeling amazing.

It is just one small piece of a larger puzzle that is your entire health.

I’ve seen patients with low Free T4 levels who are asymptomatic, and I’ve seen patients with Free T4 levels in the upper 1/3 range who feel terrible . ​

Like other tests in medicine, it needs to be used in conjunction with your symptoms and other lab tests.

But before we get into the nitty-gritty, let’s talk about how to look at your own Free T4 level…

Consider the example below:

​Going off of lab tests alone you can see that this patient’s Free T4 levels fall within the lower 1/3 of the reference range. (Ignore her other lab values, we will get into those later)

If your Doctor were to see these labs he would absolutely tell you that your lab tests were “normal”, but is that really the case? 

In treating hundreds of patients I can tell you honestly that MOST patients feel significantly better when their Free T4 levels are towards the higher range, usually in the upper half.

And this correlates well with newer studies that show that patients with hypothyroidism require a higher free T4 to achieve a normal TSH (1). 

This study showed that, while treating patients with hypothyroidism, the goal should be to obtain a free thyroxine level in the upper part of the reference range . 

​ If you recall from basic Thyroid physiology , your Free T4 levels act as a reservoir or pool to draw upon when your body needs to create the active thyroid hormone Free T3 . 

So when thinking logically about this…

As your free T4 level increases, the more you can draw upon this pool to create the active hormone… right?

It turns out that this is the way that most Doctors (and subsequently patients) think about the thyroid.

Unfortunately, for at least 15% of the population, it isn’t true (2).

And that leaves us with a big problem:

We are basing treatment recommendations on an incomplete picture and we are wondering why our thyroid patients feel terrible and are so unhappy (3).

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Your Free T4 and Thyroid Function

Here’s where things can get a little bit tricky, and why many Doctors may actually be telling you that your thyroid is “fine” when it really isn’t. 

I just said that high levels of Free T4 are good, right?

But that isn’t always the case. 

Refer back to what I said before about Free T4 being a reservoir for Free T3. 

What if you AREN’T converting T4 to T3? (What if your body isn’t utilizing that T4 correctly?). 

Well, let’s just think about this logically again using this example:

I want you to think about your thyroid as a Dam . 

Under normal circumstances, a Dam acts to hold back A LOT of water and only lets a certain amount of water go through in a controlled fashion. 

In this example, the pool of water behind the dam is your Free T4 level, and the water going through is your Free T3. 

What will happen to the system if you suddenly can’t let any water through? 

It all backs up, and the water behind the Dam continues to grow and grow. 

Well…

The same thing happens to your Free T4 level when there is a ‘kink’ in the system. 

But instead of water, your Free T4 level goes higher and higher…

Do you see the problem now?

A kink in the conversion process may actually cause your Free T4 levels to RISE and make you think that your thyroid function is normal when the exact opposite is happening . 

As your Free T4 level rises (because it can’t convert to Free T3) it shows up as high levels of Free T4 in the serum. These high levels of Free T4 actually act to suppress your TSH (because your pituitary doesn’t have the same deiodinases as the rest of the body (4)).

So your lab tests may look something like this:

• High Free T4
• Low total T3 and free T3
• High reverse T3

Meanwhile, you are feeling terrible with every hypothyroid symptom in the book . 

Does this scenario sound familiar?

Don’t worry…

If it is happening to you we are going to discuss how to correctly diagnose it, but first, we need to talk about how T4 can be beneficial. 

Does Your T4 Even Matter?

​It’s easy to think that T4 doesn’t mean much because it isn’t the active thyroid hormone in your body . 

And it makes sense, but there is still some value in using and testing for it.

T4 levels give you an idea about how you are converting T4 into T3.

In keeping with the analogy I described above, your T4 level helps you to understand how your body is processing your T4 and T3 thyroid hormones (5).

High levels of T4 with correspondingly low levels of T3 may indicate that you need to focus on improving your T4 to T3 conversion.

You can read more about how to naturally increase your T3 levels and thus thyroid conversion here . ​

T4 levels can give you an idea if you are properly absorbing thyroid hormone (6).

Another huge benefit of testing your T4 levels is understanding if your body is actually absorbing your thyroid hormone. 

Naturally, your T4 levels should increase as you take thyroid hormone (though it is important to realize that your symptoms may not improve just because your T4 level increases).

By testing your T4 level both before and after you start thyroid hormone (this only applies to T4 only thyroid medication) you can get a rough idea as to whether or not you are absorbing the medication .

Believe it or not, absorption of thyroid hormone is a big deal and something that is frequently missed (7).

You can learn more about how to properly take your thyroid medication in this post which explains how changing the time of day you take your thyroid medication can actually improve thyroid absorption and thyroid function. 

T4 levels can help you determine if you need to focus on improving your thyroid conversion vs increasing thyroid hormone production.

This is primarily helpful for patients who know that they have hypothyroidism, but whose physician is unwilling to treat them with thyroid hormone. 

Most physicians are willing to at least test both TSH and free T4 levels which can give you, as the patient, a lot of information.

If you know that your T4 and T3 levels are low then you can focus on  taking supplements and taking action to increase your thyroid hormone production .

On the other hand, if your T4 levels are high and your T3 levels are low – you as the patient can focus on taking  supplements designed to boost T4 to T3 conversion .

Over 13 nutrients are involved in thyroid hormone production  (8) and some supplements may help thyroid conversion. 

It turns out that many patients (even those on thyroid hormone) have deficiencies in some of these nutrients which may lead to poor thyroid hormone production and conversion.

If you have Hashimoto’s then the supplements you should consider using are slightly different from the list above and you  can find more information on which supplements are best for autoimmune thyroiditis here . 

​T4 levels can help you determine if you would benefit from adding T3 thyroid medication. 

Let’s say that you are taking T4-only thyroid medication (like Synthroid) and your T4 level is high (so you know you are absorbing it) but your T3 level is still low and you are still having symptoms of hypothyroidism. 

Even in the presence of a low reverse T3 (which means you are still converting thyroid hormone ok), this may indicate that you might benefit from the addition of T3 thyroid hormone. 

Recall that T3 thyroid hormone is the most powerful thyroid hormone and is responsible for all of the good things that thyroid hormone does in your body. 

So remember:

While T4 isn’t the best thyroid test, it can still give you plenty of helpful information – especially if your Doctor isn’t willing to order the complete thyroid panel . ​

How T4 Changes with Thyroid Medication

Another very important factor is understanding how your free T4 level changes with different types of thyroid hormone.

This is worth mentioning because it isn’t always intuitive and it can lead some patients into thinking that they are not heading in the right direction even though they might be . ​

T4 on Levothyroxine (Synthroid, generic Levothyroxine, Tirosint)

The way your T4 level changes when taking T4-only thyroid medication is actually quite intuitive.

Assuming you are absorbing enough thyroid hormone, your T4 level should increase as your increase your T4 dose.

Makes sense right?

Sometimes, though, this doesn’t happen and even if it does it doesn’t necessarily mean everything is “all good”.

As I mentioned above, your T4 level might NOT raise if your dose isn’t high enough and/or if you aren’t properly absorbing the medication you are taking.

And, even if it does, there are studies showing (9) that patients who take T4-only thyroid medication show lower T3 levels than healthy populations – indicating that many patients just don’t do well on these T4-only thyroid medications. 

There are ways that you can improve the function of thyroid hormone if you are taking T4-only thyroid medication and not feeling better:

1) Consider switching to Tirosint. 

Tirosint contains 3 inactive ingredients and can help increase the absorption and effectiveness of thyroid hormone. 

The case can even be made that you should consider switching over to Tirosint if you are currently taking Synthroid or levothyroxine. 

2) Consider switching to 50mcg increments of Levothyroxine

The 50mcg tablet of levothyroxine contains the fewest inactive ingredients out of all of the other Levothyroxine dosages (For example the 100mcg tablet and so on). 

Changing your dose from 1, 100mcg tablet of levothyroxine to 2, 50mcg tablets of levothyroxine may help increase absorption and reduce any symptoms you may be having. ​

3) Consider switching from Levothyroxine to Synthroid or Synthroid to Levothyroxine

While these medications may appear to be the exact same, studies have shown that they are not bioequivalent (10). 

What this means is that your body may process them differently which may result in varying thyroid levels. 

This is an easy test because all you have to do is switch from taking one medication to the other and you may notice a difference. 

• Bottom line: If you are taking T4-only thyroid medication (Synthroid, Levothyroxine, Levoxyl) then your free T4 level should increase. If it doesn’t then you may have an absorption issue and you may benefit from switching to Tirosint. 

T4 with NDT (Armour, WP thyroid, Naturethroid)

The way that T4 changes with NDT aren’t as straightforward as it is with T4-only medications.

Any thyroid medication that contains T3 thyroid hormone, at high enough doses, will generally cause your free T4 level to drop (11). 

The degree of how much it lowers largely depends on the dose of T3 you are taking. 

The higher the dose of T3 the lower your free T4 will go. 

The reason for this has to do with how T3 and T4 influence pituitary function. 

T3 thyroid hormone is 3-4 times more potent at lowering the TSH (12) than T4 is alone. 

As your TSH lowers your body produces less T4 thyroid hormone by itself (and becomes more reliant upon medications to supplement thyroid hormone levels). 

As long as you have a functioning thyroid gland (assuming it isn’t taken out or destroyed by radioactive ablation) then your thyroid will be producing SOME T4 and T3 even if you are taking thyroid medication .

But as you increase the dose of T3 you are taking then that amount your thyroid produces drops. ​

​This will usually result in a decrease in your Free T4 level. 

As you know NDT (natural desiccated thyroid) contains mostly T4 and some T3.

This ratio is close to 80% T4 and 20% T3, which means that the medication is still mostly T4 thyroid hormone.

But even that small amount of T3 is enough to shoot up T3 levels and drop T4 levels in the body.

One mistake I see patients (and doctors make) is increasing the NDT dose while trying to get to some mythical and optimal T4 level in the serum.

In some ways this is futile, as you increase your NDT dose it will drive down your T4 level in the serum which leads to higher and higher levels of NDT.

This can actually backfire and result in high levels of reverse T3 and very high levels of free T3 . 

If you are taking 4+ grains of NDT and still experiencing symptoms of hypothyroidism, then this may be happening inside your body. ​

• Bottom line: With lower doses of NDT your free T4 level may actually drop somewhat. Higher doses of NDT (greater than 4 grains) will usually cause the free T4 to increase but this isn’t necessarily helpful. 

T4 with T3 Medications Like Cytomel and Liothyronine

This is where things get really interesting. 

Taking T3-only thyroid medication like Cytomel or liothyronine will cause your free T4 to drop below the “normal” range completely and even flag as low.

This has to do with the fact that you are suppressing the TSH with the T3 and so endogenous production of T4 decreased dramatically.

Taking T3-only thyroid medication also causes reverse T3 levels to drop too low levels as well (this is usually a good thing).

To recap what happens on T3-only thyroid medication:

• TSH level falls
• Free T3 level increases
• Free T4 level decreases
• Reverse T3 level drops

What you really need to get out of all of this is the fact that your free T4 levels do not necessarily need to be in some magical “optimal” range for you to feel good. 

Basing your treatment on these ranges may lead to suboptimal treatment as you chase all the wrong results. 

Instead of laser focusing on your free T4, make sure that you look at your T4 in context with other thyroid lab tests . 

• Bottom line: Taking T3-only thyroid medication will dramatically reduce your free T4 level and this isn’t necessarily a bad thing. 

Symptoms of Low T4 & T3

​Low free T3 and free T4 levels may indicate low thyroid function, but they may also indicate a condition known as euthyroid sick syndrome or low T3 syndrome . 

This condition is very similar to hypothyroidism, but some patients with it may not experience symptoms, whereas all patients with hypothyroidism will experience symptoms. 

If you suffer from low T3 and/or low T4 then you are also very likely to experience all of the symptoms of hypothyroidism, but with some other slight changes. 

Symptoms of low T3 and low T4 include:

• Constant fatigue
• Reduced response to T4-only thyroid medications
• Weight gain (even while on thyroid medication) 
• Low resting heart rate
• Low body temperature

Many of these symptoms result from low T3 levels directly or from the reduced conversion of T4 to T3. 

Patients who are taking thyroid medication (who still have low T4 levels) may experience many of these symptoms (13) which should spark a further investigation by your physician.

If you fall into that category make sure that you properly evaluate how effective your conversion is, and how effective your native thyroid hormone production is (use examples above). ​

Why you need the Complete Thyroid Panel

Because testing for thyroid hormone levels isn’t always intuitive, it’s very important that each time you check your thyroid levels you obtain a complete panel. 

While not all lab tests may be necessary EACH and every time you get blood work, it’s still a good idea to get all of these tests to create baseline values that you can compare further testing to. 

Let’s go back to the initial example we used at the beginning of this post:

At first glance, you may be thinking that this patient is completely normal. 

Her TSH is in the 1-2 range, her Free T3 is in the mid-range, and it’s only her Free T4 that is in the low range.

But she is actually quite hypothyroid and I know this because I treated her!

It isn’t until you order her Reverse T3 level that you finally get a better picture as to what is happening…

​Once you see and understand her Reverse T3 level you begin to understand her thyroid physiology.

The only reason her Free T3 levels even look moderately normal is that her Reverse T3 levels are inappropriately blocking any Free T3 that she has.

Remember that Reverse T3 and Free T3 both compete for cellular binding (14).

If you take into account her high Reverse T3 level, her Free T3 level suddenly starts to make more sense. 

In her case, her Free T4 level never got into the ‘optimal high’ range, but you can definitely tell that it is also inappropriately high for her, given that she can barely convert T4 to T3. 

​The bottom line:

You need a Complete Thyroid Panel if you want to have ANY idea of what is going on with your thyroid .

That means you need the following tests:

• Thyroid Antibodies
• Sex hormone-binding globulin

​And remember:

Just ordering the tests isn’t going to be enough.

You need to make sure that you and your Doctor know how to actually interpret them so you don’t fall victim to the trap I just showed you above. ​

Conclusion + Recap

Your Free T4 levels can give you amazing insight into how well your Thyroid is functioning, but you need to remember that they are only a small piece of an even larger puzzle. 

It is possible that your Free T4 levels may be inappropriately elevated ​and that isn’t always a good thing. 

If your Free T4 levels are high and you still feel terrible, then you need to make sure you are also checking your Free T3 levels and your Reverse T3 levels.

​Using these lab values together, in combination with your symptoms, will help you to understand how well your thyroid is functioning. 

So what should your T4 levels be?

If you aren’t taking thyroid hormone, then optimal levels are generally in the upper 50% of the reference range .

If you are already taking thyroid hormone then the upper 50% of the reference range doesn’t always hold, instead, you need to be focusing on other factors . 

Now I want to hear from you: 

Are your free T4 levels high but you still feel terrible?

Is your doctor willing to order the RIGHT tests?

What has helped you feel better in this situation?

Leave your comments or questions below!

Scientific References

#1. https://www.ncbi.nlm.nih.gov/pubmed/18753096

#2. https://www.ncbi.nlm.nih.gov/pubmed/19190113

#3. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3169863/

#4. https://www.ncbi.nlm.nih.gov/pubmed/6595194

#5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3887425/

#6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3857600/

#7. https://www.ncbi.nlm.nih.gov/pubmed/28153426

#8. https://www.ncbi.nlm.nih.gov/books/NBK285550/

#9. https://academic.oup.com/jcem/article-lookup/doi/10.1210/jc.2016-2660

#10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3565118/

#11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5873391/

#12. https://www.ncbi.nlm.nih.gov/pubmed/402379

#13. https://www.ncbi.nlm.nih.gov/pubmed/29381251

#14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5869352/

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Thyroid Blood Tests: Free T4 & TSH Levels

Pedro Pinheiro, MD

Updated January 22, 2024

comment 2 Comments

Summary of the Article : TL;DR

• What is the thyroid? : A butterfly-shaped gland located in the neck, it produces thyroid hormones (T3 and T4).
• What is hypothyroidism? : A condition in which there is insufficient production of thyroid hormones.
• What is hyperthyroidism? : A condition in which there is an excess production of thyroid hormones.
• Diagnosis : Made through the measurement of thyroid hormones in the blood, mainly TSH and free T4.
• What are Free T4 and Free T3? : Active fractions of the T3 and T4 hormones, which effectively modulate metabolism.
• What is TSH? : A pituitary hormone, it regulates the production of T3 and T4 by the thyroid.
• Normal TSH values : 0.4 to 4.5 mU/L.
• Normal Free T4 values : 0.7 to 1.8 ng/dl.
• What elevated TSH indicates : Usually hypothyroidism, but can also be a pituitary issue.
• What very low TSH indicates : Usually hyperthyroidism, but can also be a pituitary issue.

Hypothyroidism and Hyperthyroidism

Hypothyroidism is a condition caused by an underactive thyroid gland, resulting in insufficient production of thyroid hormones. Hyperthyroidism, on the other hand, is a condition caused by an overactive thyroid gland, resulting in an excess production of thyroid hormones.

Although hypothyroidism and hyperthyroidism are different diseases and have different symptoms, both are diagnosed by measuring thyroid hormone levels in the blood, specifically TSH and free T4.

In this article, we’ll explain the thyroid hormones and how to interpret their levels in blood tests.

How Does the Thyroid Gland Work?

The thyroid is a butterfly-shaped gland located at the base of the neck. It captures iodine consumed in food and combines it with an amino acid called tyrosine to synthesize two hormones known as triiodothyronine (T3) and thyroxine (T4).

The T3 and T4 synthesized by the thyroid are released into the bloodstream, where they act on all the cells of our body, regulating their metabolism, dictating how cells transform oxygen, glucose, and calories into energy.

• When the thyroid produces too much T3 and T4, our metabolism speeds up.
• When the thyroid produces too little T3 and T4, our metabolism slows down.

Generally, of the total hormones produced by the thyroid, 80% are T4 and 20% are T3. Although produced in smaller quantities, T3 is a much more potent hormone than T4, with its blood concentration directly dictating the body’s metabolic rate.

T4 is actually a prohormone, meaning it is a precursor to T3. 80% of the T4 released into the bloodstream, when reaching organs or tissues such as the liver, kidneys, spleen, muscles, or fat, is converted into T3 to be utilized by the cells.

Therefore, T3 is the thyroid hormone that effectively acts in our body, originating predominantly from circulating T4. Only a tiny portion of the active T3 is directly produced by the thyroid.

What is Free T4?

Over 99% of circulating T4 and T3 are bound to a protein called thyroxine-binding globulin (TBG).

These TBG-bound hormones are inert and cannot be used by organs and tissues. Therefore, only a tiny fraction, called free T4 and free T3, are chemically active and can modulate the body’s metabolism. Only free T4 can be transformed into T3 in organs and tissues.

In summary:

• The T3 hormone is the one that effectively acts on body cells, modulating metabolism.
• Most of the active T3 is derived from the conversion of T4 in peripheral tissues.
• Since more than 99% of T4 is bound to TBG, only a tiny fraction of free T4, less than 1%, provides T3 for the body’s organs and tissues to use in their cells.

In conclusion, measuring free T4 in the blood is the test that really gives us an idea of how much potentially viable thyroid hormone is in the circulation. If there is too much circulating free T4, there will be too much T3 production in the organs, leading to hyperthyroidism. If there is too little circulating free T4, there will be a lack of T3 in the tissues, resulting in hypothyroidism.

In clinical practice, the measurement of free T4 is more valuable than the measurement of T3 or free T3 in most cases.

What is the Role of TSH?

The amount of T3 and T4 produced by the thyroid gland is carefully regulated by the central nervous system, specifically the pituitary gland, located at the base of the brain.

In people with a healthy thyroid gland, the amount of free thyroid hormone in the blood is kept at a level that is neither too high nor too low. When there is too much free T4 in the blood, the thyroid gland reduces its production of T3 and T4. On the other hand, if there are signs that free T4 levels are becoming insufficient, the thyroid gland quickly begins producing more T3 and T4 to keep the body’s metabolism from slowing down.

The signal for the thyroid to increase or decrease its production of T3 and T4 comes from the pituitary gland, via a hormone called thyroid stimulating hormone (TSH).

See the figure above and follow the reasoning. When circulating levels of thyroid hormones (T3 and T4) are low, the pituitary gland detects this shortage and responds by increasing the secretion of Thyroid Stimulating Hormone (TSH). This elevation in TSH signals the thyroid gland to enhance the production of T3 and T4.

As the concentrations of T3 and T4 rise to optimal levels, the pituitary gland recognizes this equilibrium and correspondingly decreases TSH production. This reduction in TSH lessens the stimulation of the thyroid gland, thereby preventing the overproduction of thyroid hormones.

The interplay between TSH and free T4 levels is a finely tuned mechanism. The pituitary gland continually adjusts TSH concentrations to maintain a delicate balance. It ensures sufficient thyroid hormone production to meet the body’s needs while avoiding excessive stimulation of the thyroid gland.

What are the Normal Values of TSH and Free T4?

In most cases, the TSH and free T4 measurements are enough to assess the functioning of the thyroid.

Before we explain how to interpret the results of these two hormones, we need to know their reference values (these values can vary slightly from one laboratory to another).

• Normal TSH values : 0.4 to 4.5 mU/L (some centers accept up to 5.0 mU/L as an upper value).
• Normal free T4 values : 0.7 to 1.8 ng/dl.

Note : A study by the National Academy of Clinical Biochemistry suggested that the normal range for a healthy thyroid should be up to 2.5 mU/L. This is because they found that 95% of the healthy people they tested had thyroid levels (TSH levels) between 0.4 and 2.5 mU/L. However, another study from Germany, which also carefully selected participants, found the normal range to be slightly wider, from 0.3 to 3.63 mU/L. If we start using 2.5 mU/L as the upper normal limit for TSH, it means that many more people could be diagnosed with a mild form of low thyroid function, known as subclinical hypothyroidism. However, no clear evidence exists that TSH levels between 2.5 and 5.0 mU/L are harmful. So it’s debatable whether we should label people with these levels as having a thyroid problem.

The latest method for measuring TSH is known as the Third-generation TSH chemiluminometric assays. This advanced technique is more sensitive than earlier versions, allowing it to detect very low TSH levels, down to 0.01 mU/L. This improvement means it can identify even the smallest changes in TSH levels in the body.

What Does It Mean to Have an Elevated TSH Level?

TSH levels rise whenever the pituitary gland senses a drop in circulating thyroid hormone levels.

In patients with hypothyroidism, the pituitary needs to maintain higher than normal TSH levels (above 4.5 or 5 mU/L) to constantly stimulate the thyroid to increase its production of T3 and T4.

Different Scenarios of High TSH:

Subclinical Hypothyroidism

If the thyroid disease is still mild and the elevation of TSH can stimulate the production of thyroid hormones to keep them at adequate levels, the patient will not show any symptoms, as the symptoms of hypothyroidism only appear when free T4 levels are low. This is the case of subclinical hypothyroidism, which is an early form of hypothyroidism (suggested reading: Subclinical Hypothyroidism ).

Overt hypothyroidism

If the thyroid disease is severe, no matter how much the pituitary increases TSH production, the patient’s thyroid will be unable to respond by producing more thyroid hormones to normalize blood levels. In these cases, the patient has elevated TSH, generally above 10.0 mU/L, and low levels of free T4. As their free T4 is low, the patient usually has the typical symptoms of hypothyroidism.

Patients with untreated hypothyroidism can have very high levels of TSH, sometimes above 100.0 mU/L.

Central Hyperthyroidism

This condition occurs when TSH and free T4 levels are both elevated.

The issue in this scenario is with the pituitary, not the thyroid. The pituitary produces too much TSH despite already high levels of thyroid hormones in the blood, leading to symptoms of hyperthyroidism. This pituitary-driven hyperthyroidism is less common than thyroid-related hyperthyroidism.

In Summary, What Could a High TSH Level Indicate?

• Subclinical Hypothyroidism : Mild thyroid disorder with slightly elevated TSH (5.0-10.0 mU/L) but normal thyroid hormones (T3 and T4), presenting no symptoms.
• Clinical Hypothyroidism : Advanced thyroid disease with very high TSH (often above 10 mU/L) and low T4 levels, leading to typical hypothyroidism symptoms.
• Central Hyperthyroidism : Uncommon condition where both TSH and T4 are high, caused by pituitary dysfunction, resulting in hyperthyroidism symptoms.

What Does It Mean to Have a Low TSH Level?

The logic applied to low TSH is the same as that for high TSH. If there is an abundance of thyroid hormone circulating in the blood, the pituitary gland responds by decreasing its release of TSH, thereby reducing the stimulation of the thyroid.

Similarly, there are three distinct situations that can occur when TSH levels are low:

Subclinical Hyperthyroidism

In cases where the thyroid is overactive, TSH levels plummet to halt further stimulation of the gland. In subclinical hyperthyroidism, TSH is typically below 0.4 mU/L, but free T4 levels remain normal. This occurs because the gland is highly responsive, and minimal amounts of TSH are enough for the thyroid to produce hormones. Therefore, patients usually do not show symptoms at this stage.

Overt Hyperthyroidism

Certain conditions can cause the thyroid to become excessively active and operate independently of the pituitary gland, producing hormones even without TSH stimulation.

When there’s a high level of free T4 in the bloodstream, the pituitary is essentially “inhibited”, producing almost no TSH, with blood levels below 0.1 mU/L. The patient therefore has very low levels of TSH, but high levels of free T4, resulting in overt hyperthyroidism.

Central Hypothyroidism

When both TSH and free T4 levels are low, it suggests a normally functioning thyroid that is adequately responding to reduced TSH levels.

The problem primarily resides in the pituitary gland. Despite low free T4 levels, the pituitary fails to sufficiently elevate TSH secretion to stimulate the thyroid into producing additional hormones, thus safeguarding the patient from developing hypothyroidism.

This type of hypothyroidism, stemming from the pituitary gland, is less common compared to hypothyroidism that originates directly from the thyroid.

In Summary, What Could a low TSH Level Indicate?

• Subclinical Hyperthyroidism : overactive thyroid, leading to TSH levels falling below 0.4 mU/L to minimize gland stimulation, while free T4 levels remain normal. Patients usually don’t exhibit symptoms.
• Overt Hyperthyroidism : the thyroid gland becomes excessively active and functions independently of the pituitary gland. This results in a high concentration of free T4 and extremely low TSH levels (below 0.1 mU/L), leading to obvious symptoms of hyperthyroidism due to the elevated free T4.
• Central Hypothyroidism : both TSH and free T4 levels are low, indicating a normally functioning thyroid that’s responding appropriately to reduced TSH. The underlying issue is with the pituitary gland, which fails to increase TSH production in response to low T4.
• Laboratory assessment of thyroid function  – UpToDate.
• Thyroid Function Tests  – American Thyroid Association.
• Assessment of Thyroid Function: Towards an Integrated Laboratory – Clinical Approach  – The Clinical biochemist. Reviews.
• American Thyroid Association guidelines for use of laboratory tests in thyroid disorders  – JAMA.

Dr. Pedro Pinheiro

Pedro Pinheiro holds a medical degree from the Federal University of Rio de Janeiro (UFRJ) and is a specialist in Internal Medicine and Nephrology, certified by the State University of Rio de Janeiro (UERJ) and the Brazilian Society of Nephrology (SBN). He is currently based in Lisbon, Portugal, with his credentials recognized by the University of Porto and the Portuguese Nephrology Specialty College.

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2 responses to “thyroid blood tests: free t4 & tsh levels”.

Levothyroxine (T4): This is the synthetic form of thyroxine (T4) and is the treatment of choice for hypothyroidism. It helps replace or supplement the T4 produced by the thyroid gland, which the body can convert to T3 as needed.

Liothyronine (T3): This is the synthetic form of triiodothyronine (T3). In some cases, especially when the conversion of T4 to T3 is insufficient, liothyronine may be administered to provide T3 directly.

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The articles published on MD.Saúde are for informational purposes only. The site's content should not be used as a substitute for clinical diagnosis or treatment without consulting a doctor, nutritionist, or other appropriate healthcare professional.

© MD.Saúde 2008 - 2024

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Upstudy thothai solution, step-by-step solution, quick answer, related questions.

Solve the inequality for \( v \). \[ -5 \leq \frac{v}{-5} \] Simplify your answer as much as possible \( \square \)

Find the vertical asymptotes (if any) of the graph of the function. (Use \( n \) as an arbitrary integer if necessary. If an answer does not exist, enter DNE.) \[ h(t)=\frac{t^{2}-2 t}{t^{4}-16} \]

(5) \( 0.04=\frac{4}{100}= \)

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What Is a Total Thyroxine (T4) Test?

What to expect when undergoing this test

Purpose of Test

Before the test, during the test, after the test, interpreting results.

The total thyroxine test is used to diagnose thyroid disorders . Thyroxine (T4) is a thyroid hormone, and the test measures how much is in your blood. Some thyroid diseases are tied to too little T4, and others are tied to too much.

Other names for this test are a total T4 test, total T4 concentration, and a thyroxine screen.

The thyroid is a gland in the front of your throat that makes hormones and regulates a variety of important functions including energy use, weight, body temperature, and mood.

T4 functions in your body in a couple of forms. One form bonds with a protein to perform certain tasks and another form doesn't, which allows it to perform different jobs. The total T4 test checks total T4 levels, which includes both forms and free T4, which is the form not bonded with a protein.

The level of total T4 is greatly dependent on the amount of binding protein in the blood, and the amount of protein is influenced by many nonthyroid conditions. So the total T4 measurement may not accurately reflect the condition of the thyroid. For this reason, the free T4 test, which measures only the active, unbound portion of T4 in the blood, is considered a much superior test, and it has largely supplanted the total T4 test in clinical medicine.

Your healthcare provider may order a total T4 test if you have symptoms that could indicate hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), especially if you have other risk factors such as being female and over the age of 60 or you have family members with thyroid disorders .

Your healthcare provider will likely order other measurements of thyroid function at the same time as a T4 test.

These generally include tests of thyroid stimulating hormone (TSH) and triiodothyronine (T3). Tests to look at antibodies that could indicate autoimmune disease may also be done at the same time or may be done as a follow-up to abnormal thyroid-function tests .

Low levels of T4 could lead to more testing to determine whether you have an autoimmune thyroid disease called Hashimoto's thyroiditis. High levels may lead to testing for Graves' disease , thyroiditis, or goiter.  

The T4 and other thyroid tests are performed on blood samples. Taking blood samples is fairly quick, simple, and low risk.

The most common risks people face from a blood test is slight pain or mild bruising afterward, which should go away quickly.

Some people, especially those who are afraid of needles, may experience dizziness, nausea, or ringing in the ears during or immediately following a blood draw. If this happens to you, let someone at the medical center know. Most facilities are well equipped to deal with this reaction, which usually involves lying down for a while and drinking some water.

If you have a history of negative reactions, you may want to arrange for someone to drive you to and from the test facility.

Let the nurse or phlebotomist who is drawing your blood know before the test if you've had bad reactions to blood draws in the past, you have a bleeding disorder or are taking blood-thinning medications, or if your skin tears or bruises easily. They should be able to mitigate any risk these elements may create.

Blood for T4 and other thyroid tests can generally be drawn at any time of day. It doesn't require fasting (avoiding food) beforehand.

Be sure to have your insurance card and any written orders your healthcare provider may have given you.

Talk to your healthcare provider about any medications you're taking and whether they could alter your test results.

• You may need to take a break from certain medications, if your endocrinologist advises it. These include:
• Some cancer drugs
• Thyroid medications (unless you're being checked for how effective the medication is)

Other drugs may impact results as well, and so could supplements, so make sure your healthcare provider is aware of everything you're taking. Biotin, in particular, interferes with thyroid assays. Patients should stop biotin three days before a thyroid test, especially if the dosage is exceeding 5,000 mcg per day.

Birth control medications as well as pregnancy can also affect your thyroid hormone levels, so make sure your healthcare provider knows if you are or could be pregnant.

Timing and Location

The blood draw itself should just take a few minutes. If you're getting multiple tests, it could take slightly longer. If the blood is being drawn in your healthcare provider's office during an appointment, it should add very little time to the appointment length.

Going to a lab for the test can require a larger time commitment. If you have a scheduled time for your test, be sure to arrive early enough to check in and pay any copays that may be due at the time. If you're anxious about the test, you may also want to give yourself a few minutes to sit calmly and relax.

Labs are often busy, so if you're dropping in, you may want to call ahead of time or aim for a time of day (such as early in the morning) when they tend to be less crowded.

What to Wear

You should be able to stay in your own clothing for the blood draw. Your arm will need to be exposed, so sleeves that are short or can be pushed up easily are best.

In case of a dizzy spell, you may want to wear flat shoes and clothing that's not tight and constricting.

Food and Drink

Any time you're having blood drawn, you should be sure you're well hydrated. That helps your veins keep their shape, which means it's easier to find them and successfully insert the needle.

Since you don't need to fast before a T4 test, it's a good idea to have something in your stomach, which may help avoid any nausea.

If your healthcare provider is ordering other tests at the same time, however, some could require fasting. Be sure to follow all of the instructions you're given by the practitioner and/or the lab performing the test.

Cost and Health Insurance

Typically, thyroid function tests are covered by insurance when they're deemed medically necessary. If you have any questions, be sure to call your insurance company ahead of time to see what, if any, out-of-pocket expenses you could face.

Laboratory costs for a total T4 test can range from $45 to about $130. If you're not insured, you may face additional charges on top of that, especially if your healthcare provider is ordering more than one test. A full set of thyroid tests may cost more than $500.

Your healthcare provider's office, insurance company, and lab should be able to help you determine the cost before you get the tests.

Before the blood draw, the nurse or phlebotomist may ask you to confirm certain information such as your name, birth date, healthcare provider ordering the test, and what test you've been sent for. This is to help prevent errors.

You'll be asked to expose your arm, and the insertion area will be cleaned with alcohol. The person performing the draw will tie a band around your upper arm to trap blood in your veins, which makes it easier to find a good vein and insert the needle. If your veins aren't standing out well, you may be asked to pump your fist.

Throughout the Test

Once a good vein is identified, the needle will be inserted. The band will be released to get the blood flowing again, and the vial attached to the needle will fill up. Depending on how many tests are ordered, the nurse/phlebotomist may need to change vials one or more times.

After the requisite blood has been drawn, the insertion site will be bandaged.

Most of the time, you can leave right away after a blood draw. If you have any kind of negative reaction, let someone at the facility know so you can get the proper care. Usually, even with a bad reaction, people are OK after a few minutes.

You may have a little soreness and bruising around the site where the needle was inserted, which typically goes away in a short amount of time. If you have any problems or questions, be sure to contact your healthcare provider.

Managing Side Effects

If the site is sore, you may want to ice it or take over-the-counter pain medication. You shouldn't have any other lingering effects from a simple blood draw.

In adults, the typical range for free T4 is between .9 and 2.o nanograms per deciliter. Total T4 tends to vary more with age.

An abnormally high T4 level may indicate hyperthyroidism, thyroiditis, or goiter. It may lead to additional tests for Graves' disease.

An abnormally low T4 level can be a sign of hypothyroidism, a problem with your pituitary gland, malnutrition or iodine deficiency, or other illness. It may lead to further tests for Hashimoto's thyroiditis.

However, an abnormal T4 level alone doesn't usually lead to a diagnosis. Your healthcare provider will likely analyze it along with T3 and TSH levels.

Once you have the results, your healthcare provider may want you to come back in to discuss further testing or treatment options, depending on whether a diagnosis has been made. If you don't hear back about your results in a timely manner or if you don't understand what they mean, contact your healthcare provider's office. If you are diagnosed with a thyroid disorder, then it's time to look into treatment options as early treatment is key.

A Word From Verywell

Thyroid disorders are common (especially in women) and highly treatable. Many thyroid diseases are managed by taking medication and possibly making some dietary changes. While being diagnosed with a thyroid disorder can be scary, the upside is that it means you can start treating and managing the condition, which should mean feeling and functioning better.

Shahid MA, Sharma S. Physiology, Thyroid Hormone . In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

National Institute of Diabetes and Digestive and Kidney Diseases. Hypothyroidism (Underactive Thyroid) .

National Institute of Diabetes and Digestive and Kidney Diseases. Hyperthyroidism (Overactive Thyroid) .

Sarne D. Effects of the Environment, Chemicals and Drugs on Thyroid Function . In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.

Henze M, Brown SJ, Hadlow NC, Walsh JP. Rationalizing Thyroid Function Testing: Which TSH Cutoffs Are Optimal for Testing Free T4? . The Journal of Clinical Endocrinology & Metabolism. 2017;102(11):4235-4241. doi: 10.1210/jc.2017-01322

Sheehan MT. Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed – A Review for Primary Care. Clinical Medicine & Research . 2016;14(2):83-92. doi: 10.3121/cmr.2016.1309

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By Adrienne Dellwo Dellwo was diagnosed with fibromyalgia in 2006 and has over 25 years of experience in health research and writing.