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"Full thyroid panel" is a common way to describe a group of thyroid blood tests. According to NIDDK, thyroid blood tests may include thyroid stimulating hormone (TSH), T4, T3 and thyroid antibody tests (NIDDK). Which tests are included can vary.
This guide explains, in general terms, what each of these tests measures.
How the thyroid and pituitary work together
The thyroid's main hormone is thyroxine, called T4. The body converts T4 into triiodothyronine, called T3, mainly in the liver and in tissues where T3 acts (American Thyroid Association).
How much T4 the thyroid makes is controlled by TSH, a hormone made by the pituitary gland at the base of the brain. The American Thyroid Association compares the pair to a heater and a thermostat. When the pituitary senses too little T4, it makes more TSH to signal the thyroid. When T4 rises to a certain level, TSH production shuts off (American Thyroid Association).
Tests that may be part of a thyroid panel
| Test | What it measures |
|---|---|
| TSH | A pituitary hormone that tells the thyroid how much T4 and T3 to make (NIDDK) |
| Total T4 | Both the T4 that's bound to proteins in the blood and the T4 that's free (American Thyroid Association) |
| Free T4 | Only the unbound T4 that can enter and affect the body's tissues (American Thyroid Association) |
| T3 | The hormone the body makes from T4 (American Thyroid Association) |
| Thyroid antibodies | Antibodies the immune system can make against thyroid proteins, such as thyroid peroxidase and thyroglobulin (American Thyroid Association) |
The American Thyroid Association describes TSH as the usual first test of thyroid function (American Thyroid Association).
Two tests that are often confused
Reverse T3. Reverse T3 is an inactive form of T3. The ATA says that in healthy people who aren't in the hospital, measuring reverse T3 doesn't help show whether hypothyroidism exists and isn't clinically useful (American Thyroid Association).
Thyroglobulin vs thyroglobulin antibodies. Thyroglobulin (Tg) is a protein made by thyroid cells. The ATA notes it isn't a measure of thyroid function, and is used most often to monitor people who have had surgery for thyroid cancer. Thyroglobulin antibodies are a separate test (American Thyroid Association).
What can affect thyroid test results
The American Thyroid Association notes some general factors (American Thyroid Association):
- Estrogen, from pregnancy or birth control pills, can raise total T4 and T3 by increasing the proteins that carry these hormones.
- Biotin, a common over-the-counter supplement, can make several thyroid test results appear abnormal when they're actually normal.
When to see a clinician
Questions about thyroid health, or about any change in health, are best discussed with a licensed clinician who knows a person's history. In a medical emergency, call 911 or go to the nearest emergency room.
Frequently asked questions
What's the difference between T4 and T3? T4 (thyroxine) is the main hormone the thyroid releases. The body converts T4 into T3 (triiodothyronine), mainly in the liver and in the tissues where T3 acts (American Thyroid Association).
What does "free" mean in free T4? Most T4 in the blood is bound to carrier proteins. "Free" T4 is the unbound portion that can enter and affect the body's tissues (American Thyroid Association).
What does the pituitary gland have to do with the thyroid? The pituitary makes TSH, the hormone that signals the thyroid how much T4 and T3 to make (NIDDK).
Is thyroglobulin the same as thyroglobulin antibodies? No. Thyroglobulin is a protein made by thyroid cells. Thyroglobulin antibodies are antibodies the immune system can make against that protein, and they're measured with a separate test (American Thyroid Association).
- American Thyroid Association. Thyroid function tests.
- National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Thyroid tests.
The information in this article is for general educational purposes only. It is not medical advice and is not a substitute for diagnosis or treatment from a qualified clinician who knows your history. Don't start, stop or change any treatment based on this article. If you think you're having a medical emergency, call 911 or go to the nearest emergency room. Reading this article does not create a clinician-patient relationship with Tenor Health or any provider on our platform.
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