Thyroid blood tests are an important part of diagnosing and treating thyroid disorders. Understanding results, however, takes some knowledge about what these tests check for, how they affect your thyroid, and how they do or don't interact with one another.
Without this, some of the test results can be confusing or seem contradictory, though. For instance, why does a high TSH level mean low thyroid activity? Why can you have high TSH and normal T4?
This article looks at the different blood tests for thyroid disorders and what numbers you might see in your results. It also explains why some healthcare providers prefer certain thyroid tests while others make different choices.
How to Work With Your Thyroid Medical Team
Your thyroid gland sits in the front of your throat. It's responsible for many important bodily functions, such as:
- Metabolism (breaking down food for energy)
- Heart function
- Muscle function
- Bone maintenance
When you have low thyroid function, those processes slow down. You may gain weight, feel sluggish and fatigued, and be slow to heal.
Excessive thyroid function speeds up these processes. That can mean unintended weight loss, agitation, and a racing heart.
By comparing the results of various thyroid tests, a healthcare provider can tell if you have:
- Hypothyroidism (low thyroid function)
- Hashimoto's thyroiditis (autoimmune hypothyroidism)
- Hyperthyroidism (excessive thyroid function)
- Graves' disease (autoimmune hyperthyroidism)
In autoimmune thyroid disease, your immune system mistakenly attacks healthy tissues as if they were a virus or bacteria.
Types of Thyroid Function Tests
The purpose of thyroid blood tests is tomeasurethe thyroid gland's function. This is done by looking at hormones and other substances produced by the thyroid glandand organs that control thyroid function.
A single test offers helpful information about your thyroid health, but it usually takes more than one test to get a complete picture.
Thyroid-stimulating hormone (TSH) acts as a messenger to the thyroid gland. It comes from the pituitary gland in the brain, not the thyroid itself.
What happens is:
- Your body constantly monitors thyroid hormone levels.
- If levels are low, your pituitary releases TSH.
- TSH tells the thyroid to step up hormone production.
- If levels are high, the pituitary releases less TSH.
- This signals the thyroid to reduce hormone production.
The thyroid hormones are called triiodothyronine (T3) and thyroxine (T4).
T3 is the active thyroid hormone. It tells your cells to produce more energy, along with many other functions. The thyroid produces some T3 and the rest is converted from T4 in other tissues.
Much of the T3 in your system at any given time is bound to proteins, which makes it not immediately usable by your body.
Blood tests can measure T3 in three different ways:
- Total T3:The total amount of triiodothyronine in the blood, bound to protein or not
- Free T3:Not bound to protein, usable by your tissues
- Reverse T3:An inactive form of T3 that attaches to thyroid receptorsbut can't activate them
When reverse T3 occupies thyroid receptors, it prevents free T3 from doing so. That can lead to hypothyroidism symptoms. This generally happens only when the body is trying to conserve energy due to severe illness or starvation.
T4 works as a "storage" hormone. It starts out inactive, then your body converts it to T3 when and where it's needed.
To be converted, it goes through a process called monodeiodination. That means itloses an atom of iodine to become T3. The T4 test measures two key values:
- Total T4 is the total amount of thyroxine found in the blood. This includes T4 that has bonded with protein, and T4 that has not. The difference affects its ability to enter tissues.
- Free T4 is the type not bonded to protein, so it's usable by your tissues.
Thyroglobulin (Tg) is a protein made by the thyroid gland. It's mostly measured as a tumor marker to help guidethyroid cancertreatment.
Treatment often involves thyroidectomy (surgical removal of the thyroid) or radioactive ablation (RAI)therapy to destroy the gland. A high Tg level is a sign that cancer cells are still present after these treatments.
By comparing baseline values with later results, the Tg test can tell healthcare providers if cancer treatments are working. It also tells them whether or not the cancer is in remission.
Some thyroid disorders are caused by autoimmune diseases. In these diseases, the immune system targets and attacks normal thyroid cells by mistake. Three common antibodies are associated with autoimmune thyroid disease:
- Thyroid peroxidase antibodies (TPOAb) are detected in 95% of people with Hashimoto's and around 70%of those with Graves' disease. A high TPOAb is also seen after childbirth in postpartum thyroiditis.
- Thyroid-stimulating hormone receptor antibodies (TRAb) are found in 90% of Graves' disease cases, but only 10% of Hashimoto's cases.
- Thyroglobulin antibodies (TgAb) are produced by your body in response to the presenceof thyroglobulin. One in four people withthyroid cancer will have elevated TgAb. It's also detected in 80% of people with Hashimoto's and between 50% to 70% of those with Graves'disease.
Thyroid Binding Proteins
Testing the blood level of proteins that bind to T3 and T4 can help healthcare providers understand thyroid problems in people whose glands still work normally. Three common tests are:
- Thyroid binding globulin (TBG): Measures levels of a protein that carries thyroid hormones in the blood
- T3 resin uptake (T3RU): Counts the percentage of TBG in a sample of blood
- Free thyroxine index (FTI):An older testing method using total T4 multiplied by the T3RU to check for either low or excessive thyroid function
What Is Hemoglobin Electrophoresis?
Side Effects of Thyroid Blood Tests and Care
Thyroid blood tests are performed using a routine blood draw. That's when blood is drawn from you with a syringe and sent to a lab. This is a safe procedure with few potential side effects.
It's rare, but some people get nauseous or feel faint when they have blood drawn. Let the medical personnel know immediately if you experience these side effects.
Later, you may notice a small bruise or have some tenderness at the needle insertion site. An over-the-counter pain reliever or an ice pack can help with this.
You should get medical attention if the insertion site is:
- Highly painful
These are signs of an infection, which needs to be treated with antibiotics.
Test Reference Ranges
The results of thyroid blood tests are listed with what's called a reference range. This range gives the "normal" or expected levels healthcare providers typically see from the tests.
Generally speaking, anything in this range is considered normal. Test numbers near the upper or lower limit are borderline, while anything outside of these limits is considered not normal.
In the middle of the reference range is a "sweet spot" called the optimal reference range, in which thyroid function is considered ideal.
It's important to know that reference ranges and the units of measurement used can vary from lab to lab. To ensure consistency in your test results, try to use the same lab for every test.
Test results have to be interpreted to give them meaning. The one test that arguably gives the most insight into your thyroid function is the TSH. Alongside results of free T3 and free T4 tests, the TSH may even suggest the cause of a thyroid problem.
Thyroid Disease Healthcare Provider Discussion Guide
Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.
TSH values outside of a "normal" range suggest a thyroid disorder is at work. Values at or near the upper or lower range may suggest a subclinical disorder without any symptoms.
Here's what TSH values mean, according to guidelines from the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA)
- 4.7 to 10 milliunits per liter (mU/L) = subclinical low thyroid function
- 10 mU/L or higher = symptomatic low thyroid function
- 0.1 to 0.5 mU/L = subclinical overactive thyroid function
- 0.1 mU/L and lower = symptomatic overactive thyroid function
Comparing High/Low TSH and T3/T4 Levels
By comparing TSH with T4 values, your healthcare provider may be able to see a more clear picture of the thyroid issue. For example:
- Normal TSH + normal T4 = normal thyroid function
- High TSH + normal T4 = you may have a higher risk of developing an underactive thyroid
- Low TSH + high T4 = overactive thyroid
- High TSH + low T4 = underactive thyroid
- Low TSH + low T4 = low thyroid function due to another problem, such as pituitary gland dysfunction
Looking at TSH alongside T3 test results can also help with diagnosis:
- Low T3 + high TSH = low thyroid function
- High T3 + low TSH = overactive thyroid
Other thyroid tests may be a part of a standard thyroid workup or used when needed. Some have specific aims. The others are used for screening purposes or to evaluate possible causes.
- RT3 testscan help find problems with thyroid control. People with euthyroid sick syndrome(ESS), for example, have abnormal thyroid hormone levels due to an illness not related to the thyroid.
- Tgtests can predict long-term treatment outcomes. Research has suggested only 4% of people with a Tg level under 1 will see the cancer recurafter five years.
- TPOAb testscan help confirm Hashimoto's disease if TSH is high and T4 is low.
- TRAb tests help diagnose Graves' disease, confirm a diagnosis oftoxic multinodular goiter, or, in late pregnancy, to check a baby's risk of Graves' disease or an overactive thyroid.
- TgAb tests help diagnose autoimmune disease or help clarify post-cancer treatment test results. This is because TgAb sometimes interferes with Tg readings.
Many thyroid blood tests are available, including tests of thyroid hormones, thyroid stimulating hormone, antibodies to the thyroid, and markers of thyroid cancer. Their combined results can paint a complete picture of your thyroid function.
The test results are interpreted based on a common standard for each test, all of which look at thyroid function in different ways. They can be used for diagnosis or to monitor how effective your treatments are.
A Word From Verywell
Thyroid blood test results are complex and can be confusing. The important thing is to pay attention to how your healthcare provider interprets them.
If you have abnormal results, don't panic. Thyroid disorders are common and highly treatable. Your healthcare provider can go over potential treatments with you so together you can decide together how to manage your condition.
Frequently Asked Questions
What are normal thyroid levels?
Normal thyroid levels, specifically for TSH (thyroid stimulating hormone), fall within the range of 0.5 to 5.0 mIU/L (milli-international units per liter). In adults, normal total T4 levels are between 5.0 and 12.0μg/dL (micrograms per deciliter). Also in adults, the normal range for T3 levels is between 80 and 220 ng/dL (nanograms per deciliter).
How long does a thyroid blood test take?
An average thyroid blood test only takes a few minutes. The test itself is short like many other blood tests. However, receiving the results may take some time. Be sure to ask your healthcare provider when they expect to receive the test results.(Video) TSH Results / Levels: How to explain in 80 seconds
What is the most accurate thyroid blood test?
The most accurate thyroid blood test measures your thyroid stimulating hormone (TSH). The results of this test show whether the body is telling the thyroid gland to make more thyroid hormone or less.
How do you know if you have thyroid problems?
The only way to know for certain if you have thyroid problems is to receive a diagnosis from a healthcare provider. However, there are certain symptoms associated with hypothyroidism and hyperthyroidism that may clue you in that something isn't right. A few symptoms associated with both of these conditions includes fatigue, hair loss, puffy face or eyes, and insomnia.
Do doctors go over thyroid test results?
Yes, your healthcare provider should go over the results of your thyroid test with you. If you get results online or by mail and don't understand them, get in touch with your provider.
Can caffeine change TSH levels?
It can, yes. That's because caffeine makes the thyroid drug levothyroxine move too quickly through your digestive system, so you can't absorb it properly. That can make your T4 levels fall.(Video) Thyroid Function Tests (TFTs) explained | COMPLETE GUIDE in 4 minutes!
What Do Your Thyroid Blood Test Results Mean? ›
A high TSH level most often means you have hypothyroidism, or an underactive thyroid. This means that your thyroid isn't making enough hormone. As a result, the pituitary keeps making and releasing TSH into your blood. A low TSH level usually means you have hyperthyroidism, or an overactive thyroid.How do I read my thyroid test results? ›
- 4.7 to 10 milliunits per liter (mU/L) = subclinical low thyroid function.
- 10 mU/L or higher = symptomatic low thyroid function.
- 0.1 to 0.5 mU/L = subclinical overactive thyroid function.
- 0.1 mU/L and lower = symptomatic overactive thyroid function.
TSH normal values are 0.5 to 5.0 mIU/L. Pregnancy, a history of thyroid cancer, history of pituitary gland disease, and older age are some situations when TSH is optimally maintained in a different range as guided by an endocrinologist. FT4 normal values are 0.7 to 1.9ng/dL.What do the numbers on a thyroid test mean? ›
Normal thyroid-stimulating hormone (TSH) levels generally fall between 0.4 and 4.0 milliunits per liter (mU/L). TSH levels higher than 4.5 mU/L usually indicate an underactive thyroid (hypothyroidism), and low TSH levels—below 0.4 mU/L—indicate an overactive thyroid (hyperthyroidism).What is a bad number for thyroid? ›
Ultimately, the standard of care is to treat into the goal range for TSH, which is typically between 0.5 and 4.5 or 5. A TSH level of 10 mIU/L or higher is typically indicative of hypothyroidism. A TSH level of 4.5 to 10 mIU/L is considered indicative of subclinical hypothyroidism.What is a dangerously high TSH level? ›
Some suggest that TSH levels of over 2.5 milliunits per liter (mU/L) are abnormal, while others consider levels of TSH to be too high only after they have reached 4 to 5 mU/L. Both children and teenagers as well as older people have somewhat higher TSH levels than middle-aged people.What is the ideal TSH level? ›
The normal range of TSH levels in adults is between 0.4 to 4.0 mIU/L (milli-international units per liter). Some research suggests that this range should actually be more like 0.45 to 2.5 mIU/L. The TSH range may also vary slightly based on the testing facility where your blood is being analyzed.What is the most important thyroid level? ›
Assessment of TSH is the single most useful test of thyroid function in the vast majority of patients. Primary care providers should seldom need to order any other biochemical thyroid test. In most cases the TSH will be within the normal range, and no further testing is indicated.What TSH level indicates Hashimoto's disease? ›
This study illustrates that individuals with a TSH above 2.5 should be screened for Hashimoto's disease as well as cardiovascular risk markers.What is a good TSH level for age? ›
|18–30 years||0.5–4.1 mU/L||> 4.1 mU/L|
|31–50 years||0.5–4.1 mU/L||> 4.1 mU/L|
|51–70 years||0.5–4.5 mU/L||> 4.5 mU/L|
|71–90 years||0.4–5.2 mU/L||> 5.2 mU/L|
What are early warning signs of thyroid problems? ›
- Feeling tired or lacking energy even after getting enough sleep.
- Sudden weight loss or weight gain that cannot be explained by changes in diet or exercise.
- Mood swings, irritability, anxiety, or depression.
- Sleep disturbances, insomnia, or excessive sleepiness.
Thyroid hormone levels are measured with blood tests. What is a normal TSH level in a woman? An optimal TSH level in a woman is 0.4-2.5 mIU/L. For pregnant women, that upper limit is stricter than if you are not pregnant.What is a good TSH level for a woman? ›
The normal range of TSH levels in non-pregnant adult women is 0.5 to 5.0 mIU/L.What is a low functioning thyroid level? ›
Hypothyroidism is a common condition where the thyroid doesn't create and release enough thyroid hormone into your bloodstream. This makes your metabolism slow down. Also called underactive thyroid, hypothyroidism can make you feel tired, gain weight and be unable to tolerate cold temperatures.What raises TSH levels? ›
- 1) Hypothyroidism (Underactive Thyroid) TSH often increases in response to an underactive thyroid gland (primary hypothyroidism) . ...
- 2) Iodine Deficiency or Excess. ...
- 3) Obesity. ...
- 4) Radiation Therapy. ...
- 5) Pituitary Tumors. ...
- 6) Some Toxins, Drugs, and Supplements. ...
- 7) Rare Genetic Disorders. ...
- 8) Aging.
A swollen fingertip, curved nail, and thickening skin above a nail are often signs of thyroid disease.How can I lower my TSH level quickly? ›
The best way to control your thyroid is to incorporate Vitamin A in your daily life routine. All you need to do is to consume food products that are high in Vitamin A. The most common Vitamin A rich foods are; yellow and green veggies, carrots, eggs, apricots, spinach, carrots, etc.Is higher or lower TSH better? ›
Thyroid-stimulating hormone (TSH) triggers your thyroid to release its hormones, which mainly impact your body's metabolism. High TSH levels usually indicate hypothyroidism, and low TSH levels usually indicate hyperthyroidism.Does levothyroxine lower TSH? ›
One specific medical condition in which levothyroxine doses that lower serum TSH may be intentionally employed is differentiated thyroid cancer . If TSH suppression is the goal in patients with intermediate- or high-risk thyroid cancer, higher doses up to 2.2 μg/kg body weight may be needed .What should TSH level be on Synthroid? ›
The serum TSH should be rechecked 2–3 months after starting levothyroxine with the aim of keeping TSH in the lower half of recommended range (0.4–2.5 mIU/l), though a higher reference range (1.0–5.0 mIU/l) is acceptable in elderly patients (>70 years) [Biondi and Cooper, 2008].
What are the signs and symptoms of thyroid problems in females? ›
Common symptoms are fatigue, cold intolerance, weight gain, constipation, hair loss, "brain fog," skin dryness, nail changes, and menstrual cycle changes (typically irregular cycling). Symptoms of hyperthyroidism include unintentional weight loss and a rapid or irregular heartbeat.Is 5.2 high for thyroid? ›
The standard reference range for the TSH level is anywhere between 0.30 and 5.0 uIU/mL. If your TSH level is higher than 5.0 uIU/mL, then the lab will flag you as “high,” and you may experience the symptoms listed above 5.0 uIU/mL. Values of a TSH level of more than 10.0 uIU/mL need long-term thyroid supplements.Does low TSH cause weight gain? ›
People with hypothyroidism may experience a wide range of mild to severe symptoms that usually vary from one patient to another. The most common symptoms include: Weight gain: Unexpected weight gain, often accompanied by persistent fatigue, is among the earliest signs of hypothyroidism.How to tell the difference between Hashimoto's and hypothyroidism? ›
The main difference between Hashimoto's and hypothyroidism is the cause of each condition. Hashimoto's disease happens when your immune system attacks your thyroid gland. Hypothyroidism occurs when your thyroid is underactive and not producing enough thyroid hormone. And this can happen for many different reasons.Is Hashimoto's thyroid high or low? ›
What is Hashimoto's disease? Hashimoto's disease is an autoimmune disorder that can cause hypothyroidism, or underactive thyroid. Rarely, the disease can cause hyperthyroidism, or overactive thyroid.What does a Hashimoto's flare feel like? ›
Symptoms of a Hashimoto's Flare-Up
Constipation. Dry skin. Puffy face. Muscle aches.
Fatty foods – Fats are known to upset your body's ability to absorb thyroid replacement hormones. Fats can also prevent the thyroid's natural ability to produce hormones. Physicians recommend that you cut out all fried foods and limit your intake of fats from butter, mayonnaise and fatty meats.What fruits are good for hypothyroidism? ›
Tropical fruits such as mangos, papaya, and pineapple are higher on the glycemic index. Fruits like blueberries, raspberries, blackberries, strawberries, oranges, apples, and pears are lower on the glycemic scale. Choose fruits that are lower on the glycemic index to reduce sugar intake and inflammation.How can I improve my thyroid function? ›
- Maintain Healthy Iodine Levels.
- Include Selenium-Rich Foods in Your Diet.
- Increase Your Probiotics.
- Cut Back on Your Sugar Intake.
- Exercise Regularly.
- Manage Your Stress.
Thyroid hormones also influence the quality of your skin in various ways. For example, with hyperthyroidism, you may notice itchy and dry patches of skin. Your face may feel softer and swollen. You may even notice swelling around your fingertips.
What is the main cause of thyroid problems? ›
Problems with the thyroid can be caused by: iodine deficiency. autoimmune diseases, in which the immune system attacks the thyroid, leading either to hyperthyroidism (caused by Graves' disease) or hypothyroidism (caused by Hashimoto's disease) inflammation (which may or may not cause pain), caused by a virus or ...What does thyroid fatigue feel like? ›
With thyroid fatigue, you may feel like you can't get through a day without a nap. You may sleep more than usual but still feel completely exhausted. You may not even have the energy to exercise. At times, you may fall asleep during the day or very quickly at night.What is considered a dangerously low TSH level? ›
Subclinical hyperthyroidism can be divided into two categories: Mild: Low but detectable TSH level — usually 0.1 to 0.4 mIU/L. This applies to 65% to 75% of people with subclinical hyperthyroidism. Severe: TSH level is less than 0.1 mIU/L.What causes low thyroid levels? ›
There's no way of preventing an underactive thyroid. Most cases are caused either by the immune system attacking the thyroid gland and damaging it, or by damage to the thyroid that occurs during some treatments for an overactive thyroid or thyroid cancer.What is the diet for hypothyroidism? ›
Generally, there's no hypothyroidism diet. Although claims about hypothyroidism diets abound, there's no evidence that eating or avoiding certain foods will improve thyroid function in people with hypothyroidism. However, adequate dietary iodine is essential for normal thyroid function.What foods are good for thyroid? ›
- Roasted seaweed. Seaweed, such as kelp, nori, and wakame, are naturally rich in iodine--a trace element needed for normal thyroid function. ...
- Salted nuts. Brazil nuts, macadamia nuts, and hazelnuts are excellent sources of selenium, which helps support healthy thyroid function. ...
- Baked fish. ...
- Dairy. ...
- Fresh eggs.
In the case of a borderline underactive thyroid, your TSH levels are high but your T4 reading is relatively normal (that is, between 0.5 and 5.0 mIU/L). This is also called subclinical hypothyroidism.How do you interpret T3 and T4 levels? ›
A normal T3 level might be somewhere between 100 to 200 nanograms per deciliter (ng/dL), while a normal T4 level falls between 5.0 to 12.0 micrograms per deciliter (μg/dL). Free T4, which tests for the amount of T4 that is available in the body, should range between 0.8 to 1.8 nanograms per deciliter (ng/dL).What TSH level is considered hypothyroidism? ›
TSH levels over 10mU/L indicate overt hypothyroidism. People will usually need thyroxine (T4) replacement therapy. TSH levels between 4.5 and 10 mU/L indicate mildly underactive (subclinical) hypothyroidism. People should be retested every 6 to 12 months.What should my TSH and T3 levels be? ›
The normal range of T4 is suggested to be 77–155 nmol/l, T3 to be 1.2–2.8 nmol/L and TSH to be 0.3–4 mU/l . The levels of hormones above or below the normal range indicate hyperthyroidism or hypothyroidism.
What is a healthy T4 and T3 ratio? ›
In humans, a normal thyroid gland produces ~85 mcg of T4 and 6.5 mcg of T3 daily (1). Thus, the ratio of T4:T3 that is directly secreted from the thyroid gland is around 13:1.Which is more important T4 or TSH? ›
If values are outside the range of 0.4 to 4.5 milliunits per liter (mU/L), measuring T3 and T4 should follow. However, TSH is always the best first test because it is more reliable than plasma T3/T4 levels, which tend to fluctuate.What numbers indicate Hashimoto's? ›
If your TSH level falls under 0.5 mIU/L, this indicates that you have an overactive thyroid (hyperthyroidism). Numbers above the normal range, usually 5.0 mIU/L or higher, show that you may have hypothyroidism.What causes TSH levels to drop? ›
Since thyroid hormone suppresses TSH release, high levels of thyroid hormone can cause lower-than-normal TSH levels. Rarely, issues with your pituitary gland, such as a non-functioning pituitary adenoma, can result in low TSH levels as well as low thyroid hormone levels.Can low TSH cause fatigue? ›
In people living with an underactive thyroid (hypothyroidism), the body's metabolism slows down. This can often lead to many symptoms, including lethargy and fatigue.