January 13, 2019
Health care professionals use thyroid tests to check how well your thyroid is working and to find the cause of problems such as hyperthyroidism or hypothyroidism. The thyroid is a small, butterfly-shaped gland in the front of your neck that makes two thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid hormones control how the body uses energy, so they affect nearly every organ in your body, even your heart.
Thyroid tests help health care professionals diagnose thyroid diseases such as:
- hyperthyroidism—when thyroid hormone levels are too high
- Graves’ disease, the most common cause of hyperthyroidism
- hypothyroidism—when thyroid hormones levels are too low
- Hashimoto’s disease, of the most common cause of hypothyroidism
- thyroid nodules and thyroid cancer
Health care professionals usually check the amount of TSH in your blood first. TSH is a hormone made in the pituitary gland that tells the thyroid how much T4 and T3 to make.
A high blood level of T4 may mean you have hyperthyroidism. A low level of T4 may mean you have hypothyroidism.
Health care professionals use a thyroid scan to look at the size, shape, and position of the thyroid gland. This test uses a small amount of radioactive iodine to help find the cause of hyperthyroidism and check for thyroid nodules. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.
What tests do doctors use if I have a thyroid nodule?
If your health care professional finds a nodule or lump in your neck during a physical exam or on thyroid imaging tests, you may have a fine needle aspiration biopsy to see if the lump is cancerous or noncancerous.