How to Interpret Your Thyroid Test Results

Written By: Jillian Foglesong Stabile MD, FAAFP

The thyroid is a complicated gland that lives on the front of the neck just above the collarbones. The thyroid is responsible for controlling the metabolic rate and affects a number of body systems.[1] In addition to metabolic rate, thyroid hormones also affect heart and gut functions, muscle control, and brain and bone development and maintenance. If you’re wondering how to interpret your thyroid test results, this guide is designed to help you.

Understanding Thyroid Hormones

Many types of thyroid testing are available. Each test provides different information; in some cases, multiple tests are needed to fully understand how the thyroid is functioning.

TSH

Thyroid-stimulating hormone (TSH) is one of the first hormones tested when evaluating thyroid function. TSH is produced by the pituitary gland in the brain.[2] TSH is released in response to thyroid-releasing hormone (TRH). After its release, it travels to the thyroid gland and stimulates the thyroid gland to release thyroid hormones.[3,4]

• An elevated TSH is indicative of an underactive thyroid
• A low TSH indicates an overactive thyroid
• Normal TSH generally varies from 0.27 to 4.2 uIU/mL.[2] The reference range can vary from lab to lab, so check the reference range on your report when interpreting the lab results.

High TSH levels can indicate hypothyroidism. Low levels of thyroid hormone in the body cause the body to send signals to the brain which causes the pituitary gland to release more TSH.[5] Low levels of TSH can indicate hyperthyroidism. This is not as common as hypothyroidism but can also have profound metabolic effects.[6] With hyperthyroidism, the body senses elevated thyroid hormone levels and sends signals to the brain which causes the pituitary gland to release less TSH.

Thyroxine (T4)

Thyroxine is the primary hormone released by the thyroid gland. This hormone has 2 forms: either bound to protein or free.[7] Free T4 is the active form of T4 that can move into the body tissues and have effects on the body. Normal free T4 levels range from 0.7-1.9 ng/dL.[8] The levels can vary based on age and other health conditions. Elevated free T4 levels can indicate hyperthyroidism while low free T4 levels can indicate hypothyroidism. T4 is not the active form of thyroid hormone. Your body will convert T4 into T3 which is the active form. This primarily happens in the liver and kidneys.[9]

Free Triiodothyronine (T3)

Triiodothyronine is another form of thyroid hormone and is the one responsible for most of the thyroid’s metabolic effects. Like T4, T3 comes in a bound and a free form. About 20% of T3 is released by the thyroid gland, the rest is converted in the body from T4.[9] Like other thyroid hormones, normal T3 levels vary based on age. For adults, a normal T3 level is generally 79-165 ng/dL, while a normal free T3 level is 2.3-4.1 pg/mL. Elevations in T3 usually indicate hyperthyroidism while low levels can indicate hypothyroidism. T3 levels are the last thyroid function test to change when thyroid conditions occur, so they are not used as often as other thyroid tests for making a diagnosis.[9]

Thyroid Antibodies

There are several antibodies that healthcare providers can order to evaluate autoimmune thyroid disease. In autoimmune thyroid disease, the body produces antibodies that attack the thyroid gland.

Thyroid peroxidase antibody (TPOAb) levels are usually less than 9IU/mLco. Thyroglobulin antibody (TgAb) levels are normally less than 116IU/mL. Levels of both of these antibodies can be elevated in people experiencing certain conditions, including[10]:

• Hashimotos
• Graves
• Non-thyroid autoimmune diseases
• Pregnancy
• Multinodular goiter
• Thyroid cancer
• Thyroid nodules

Reverse Triiodothyronine (rT3)

Reverse T3 or rT3 is produced by the thyroid gland, but is also created when T4 is broken down.[11] When T3 is high, rT3 is low, and vice versa. Testing for rT3 is not commonly ordered and is not recommended for routine measurement in managing patients with thyroid disease. It may be more commonly used in functional medicine practice.[11]

Thyroid Hormone Binding Globulin

Thyroid hormone-binding globulin (TBG) is a protein produced in the liver that binds T3 and T4. When TBG binds thyroid hormones, it does so reversibly. Elevated levels of TBG may lead to increased total T4 and total T3, but not usually a change in thyroid function.[12]

Interpreting Your Results

TSH alone can generally be used to screen for thyroid disease and manage patients with known thyroid disease, but to make a diagnosis of thyroid disease, additional testing is usually necessary. The following table summarizes lab testing and how it may indicate thyroid disease.

What Can Interfere With Thyroid Testing?

Biotin is a common B vitamin supplement that can interfere with thyroid hormone testing results. Biotin can give the appearance of hyperthyroidism by elevating the levels of T3 and T4 while decreasing TSH levels.[13]

Another common medication that can affect thyroid hormone testing is birth control. Birth control can affect the balance between bound and free thyroid hormones by increasing the amount of TBG and other proteins in the blood.[14] This may impact treatment for people who have thyroid disorders. While birth control doesn’t cause thyroid disease, it can alter testing and impact lab results.

Thyroid disease is common in pregnancy, but pregnancy can also affect thyroid hormone testing. Pregnancy can increase TBG, total T4, total T3, and thyroglobulin antibody levels. It can also result in low TSH and low free T3.[15] Because of the changes that occur during pregnancy, people with thyroid disease should be monitored more closely during pregnancy.

When Should You Seek Professional Guidance?

If you are experiencing the symptoms of thyroid disease, it’s important to consider testing your thyroid hormone levels and getting professional advice from a healthcare professional.

The symptoms of hypothyroidism include[16]:

• Fatigue
• Cold sensitivity
• Bowel changes
• Changes to skin and hair
• Hoarseness
• Puffiness in the face
• Weakness
• Slow heart rate
• Menstrual changes
• Memory problems
• Depression
• Weight gain

Hypothyroidism can occur at any age including in infancy. Without treatment, hypothyroidism can have profound effects on the body and even lead to coma in severe cases. Symptoms of hyperthyroidism include[17]:

• Mood swings
• Anxiety and irritability
• Insomnia
• Fatigue and weakness
• Heat sensitivity
• Goiter
• Palpitations
• Weight loss
• Bulging eyes
• Pregnancy complications
• Bowel changes

Hyperthyroidism can also have significant impacts on health and can exacerbate other health conditions. Recognizing the symptoms and seeking care for thyroid disorders is extremely important to overall health.

Lifestyle Changes to Support Thyroid Health

Thyroid disease cannot be treated with diet and supplements, but a well-rounded diet is important to metabolic health.[18] Iodine deficiency is the leading cause of hypothyroidism worldwide but is less common in developed countries. For people with Hashimoto's disease, a gluten-free diet may improve symptoms.[19]

Many supplements have been proposed to help with the symptoms of thyroid disease, but most do not have adequate studies to support broad recommendations.[18] Supplements can interfere with the absorption of thyroid medications, so it is important to discuss any medications or supplements you are taking with your healthcare provider.

FAQs About Thyroid Test Results

What are the standard thyroid tests?

TSH is the most common test used in screening for thyroid disease and is also the test used to follow treatment in most cases. If TSH is abnormal, additional testing may be necessary.

Shouldn’t I always have a full panel done when my thyroid is tested?

Not necessarily. Your healthcare provider will recommend testing based on your health conditions and symptoms. It is not generally necessary to have a full range of thyroid tests done every time your thyroid is tested.

Can medications interfere with thyroid testing?

Yes, several medications can interfere with thyroid testing and thyroid medications. It’s important to discuss all of your medications and supplements with your healthcare provider.

Taking Action Based on Your Test Results

Thyroid blood test analysis can be tricky. If your thyroid testing is abnormal or you are experiencing ongoing symptoms with normal thyroid testing, you should speak with a healthcare provider to discuss additional recommendations for treatment or testing. Your healthcare provider can help with interpreting thyroid levels and can tell you what your thyroid test results mean.

Learn More About Your Thyroid Health With Everlywell

The thyroid plays an important role in your metabolic health. Imbalanced thyroid hormone levels can cause significant symptoms and interfere with your quality of life. Thyroid blood test analysis is one of the best ways to evaluate the function of your thyroid gland and how your body is responding to it. This is a key step in understanding your metabolic health.

At Everlywell, we are here to help you in your health journey. With the at-home thyroid test, you’ll collect a blood sample and send it in for evaluation in a CLIA-certified laboratory. You’ll get your results within a few days. If you need help interpreting your results or have further questions, consider a virtual appointment with one of our credentialed healthcare providers.

1. Thyroid. Cleveland Clinic. Published December 2, 2024. Medical Citation URL.
2. Thyroid-Stimulating Hormone (TSH) levels. Cleveland Clinic. Published May 1, 2024. Medication Citation URL.
3. Shahid MA, Ashraf MA, Sharma S. Physiology, thyroid hormone. StatPearls - NCBI Bookshelf. Published June 5, 2023. Medical Citation URL.
4. Pirahanchi Y, Tariq MA, Jialal I. Physiology, thyroid. StatPearls - NCBI Bookshelf. Published February 13, 2023. Medical Citation URL.
5. Patil N, Rehman A, Anastasopoulou C, Jialal I. Hypothyroidism. StatPearls - NCBI Bookshelf. Published February 18, 2024. Medical Citation URL.
6. Schraga ED MD. Hyperthyroidism, Thyroid Storm, and Graves Disease: Practice Essentials, Pathophysiology, Epidemiology. Medical Citation URL.
7. T4 (Thyroxine) test. Cleveland Clinic. Published May 1, 2024. Medical Citation URL.
8. Normal thyroid hormone levels. UCLA Health. Medical Citation URL.
9. T3 (Triiodothyronine) test. Cleveland Clinic. Published May 1, 2024. Medical Citation URL.
10. Face GEM Ecnu,. Antithyroid Antibody: reference range, interpretation, collection and panels. Medical Citation URL.
11. American Thyroid Association. Vol 12 Issue 1 P.11-12 | American Thyroid Association. American Thyroid Association. Published January 28, 2019. Medical Citation URL.
12. Liess BD MD. Thyroid-Binding Globulin: reference range, interpretation, collection and panels. Medical Citation URL.
13. American Thyroid Association. Vol 11 Issue 12 P.3-4 | American Thyroid Association. American Thyroid Association. Published December 18, 2018. Medical Citation URL.
14. Clinic C. Can birth control cause thyroid problems? Cleveland Clinic. Published June 27, 2024. Medical Citation URL.
15. Thyroid disease in pregnancy. ARUP Consult. Published online September 1, 2023. Medical Citation URL.
16. Hypothyroidism (underactive thyroid) - Symptoms and causes. Mayo Clinic. Medical Citation URL.
17. Overactive thyroid (hyperthyroidism). National Health Service. Published April 18, 2023. Medical Citation URL.
18. Diets and supplements for thyroid disorders. British Thyroid Foundation. Medical Citation URL.
19. Piticchio T, Frasca F, Malandrino P, et al. Effect of gluten-free diet on autoimmune thyroiditis progression in patients with no symptoms or histology of celiac disease: a meta-analysis. Frontiers in Endocrinology. 2023;14. Medical Citation URL.