How to Interpret Your Thyroid Test Results

Many types of thyroid testing are available. Each test provides different information, and 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 to produce and release thyroid hormones.^[3,4]

• An elevated TSH level may indicate an underactive thyroid.
• A low TSH level may indicate an overactive thyroid.
• Normal TSH levels generally range from 0.27 to 4.2 uIU/mL.^[2] Reference ranges can vary by laboratory, so it’s important to review the range provided on your lab report.

High TSH levels can indicate hypothyroidism. Low levels of thyroid hormone in the body signal the brain to prompt the pituitary gland to release more TSH.^[5]

Low TSH levels can indicate hyperthyroidism. Although less common than hypothyroidism, hyperthyroidism can also have significant metabolic effects.^[6] In hyperthyroidism, the body senses elevated thyroid hormone levels and signals the pituitary gland to release less TSH.

Thyroxine (T4)

Thyroxine (T4) is the primary hormone released by the thyroid gland. This hormone exists in two forms: protein-bound and free.^[7] Free T4 is the active form that can move into body tissues and affect bodily functions.

• Normal free T4 levels generally range from 0.7–1.9 ng/dL.^[8]
• Elevated free T4 levels may indicate hyperthyroidism.
• Low free T4 levels may indicate hypothyroidism.

T4 itself is not the most active thyroid hormone. The body converts T4 into T3, the active form of thyroid hormone, primarily in the liver and kidneys.^[9]

Free Triiodothyronine (T3)

Triiodothyronine (T3) is another thyroid hormone and is responsible for many of the thyroid’s metabolic effects. Like T4, T3 exists in both bound and free forms. Approximately 20% of T3 is produced directly by the thyroid gland, while the remainder is converted from T4 elsewhere in the body.^[9]

• Normal total T3 levels for adults generally range from 79–165 ng/dL.
• Normal free T3 levels generally range from 2.3–4.1 pg/mL.
• Elevated T3 levels may indicate hyperthyroidism.
• Low T3 levels may indicate hypothyroidism.

T3 levels are often among the last thyroid markers to change when thyroid disease develops, which is why they are not always the primary test used for diagnosis.^[9]

Thyroid Antibodies

Healthcare providers may order thyroid antibody testing to evaluate for autoimmune thyroid disease. In these conditions, the immune system produces antibodies that mistakenly attack the thyroid gland.

Thyroid peroxidase antibody (TPOAb) levels are typically less than 9 IU/mL, while thyroglobulin antibody (TgAb) levels are generally less than 116 IU/mL. Elevated levels of these antibodies may occur in people with the following conditions^[10]:

• Hashimoto’s disease
• Graves’ disease
• Non-thyroid autoimmune diseases
• Pregnancy
• Multinodular goiter
• Thyroid cancer
• Thyroid nodules

Reverse Triiodothyronine (rT3)

Reverse T3 (rT3) is produced by the thyroid gland and is also created when T4 is broken down.^[11] Generally, when T3 levels are high, rT3 levels are low, and vice versa.

Testing for rT3 is not commonly recommended for routine thyroid disease management. However, it may be used more frequently in certain functional medicine settings.^[11]

Thyroid Hormone Binding Globulin

Thyroid hormone-binding globulin (TBG) is a protein produced in the liver that binds to T3 and T4. This binding process is reversible. Elevated TBG levels may increase total T4 and total T3 levels without necessarily affecting overall thyroid function.^[12]

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.

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.

If you are experiencing symptoms of thyroid disease, it’s important to consider testing your thyroid hormone levels and seeking guidance from a healthcare provider.

The symptoms of hypothyroidism may 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 infancy. Without treatment, hypothyroidism may have serious effects on the body and, in severe cases, can lead to coma.

Symptoms of hyperthyroidism may 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 significantly affect overall health and may worsen other medical conditions. Recognizing the symptoms of thyroid disorders and seeking appropriate care is important for long-term health and wellness.

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.

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.

The thyroid plays an important role in metabolic health. When thyroid hormone levels become imbalanced, they can cause significant symptoms and interfere with overall quality of life. Thyroid blood test analysis is one of the most effective ways to evaluate how well your thyroid gland is functioning and how your body is responding to thyroid hormones.

At Everlywell, we’re here to support your health journey. With the at-home thyroid test, you can collect a blood sample from home and send it to a CLIA-certified laboratory for analysis. Results are typically available within a few days.

If you need help interpreting your results or have additional questions, consider scheduling a virtual appointment with one of Everlywell’s credentialed healthcare providers.