This information explains thyroid function tests (TFTs). Thyroid function tests are blood tests that check the amount of thyroid hormone in your blood.
Thyroid Stimulating Hormone (TSH)
Thyroid stimulating hormone (TSH) is made and released by a gland in your brain. This hormone stimulates your thyroid to work.
TSH levels
The level of TSH in your blood shows if your thyroid is too active or not active enough. If you do not have a thyroid, your healthcare provider will still check your TSH levels. This is to see if you’re getting the right dose of thyroid hormone replacement medication.
The normal TSH range may be different depending on the lab. At MSK, the normal range is 0.60 milli-international units per liter (mIU/L) to 4.80 mIU/L.
- If your TSH level is low, you’re in a state of hyperthyroidism. This means your thyroid function is too active.
- If your TSH level is high, you’re in a state of hypothyroidism. This means your thyroid function is not active enough.
In people without thyroid cancer, the goal is to keep their TSH level within the normal range.
In some people with thyroid cancer, the goal is to keep their TSH level below the normal range. This is usually for the first few years after being diagnosed and depends on the type of cancer you have. It may lower the risk of the cancer coming back. Talk with your healthcare provider about what level is right for you.
Free Thyroxine (FT4)
Free Thyroxine (FT4) is another blood test that measures your thyroid function. It tells us how much “free” or available thyroid hormone you have in your blood. At MSK, the normal range for FT4 is 0.70 nanograms per deciliter (ng/dL) to 1.50 ng/dL.
- In people without thyroid cancer, the goal is to keep their FT4 level within the normal range.
- In people with thyroid cancer, the FT4 level may be near the upper limits of the normal range.
Thyroglobulin
Thyroglobulin (THY-roh-GLAH-byoo-lin) is a protein in your blood made by your thyroid cells. We measure your thyroglobulin level to help us monitor your cancer after treatment. If your thyroglobulin level rises, it could mean that you need more tests and follow-up care. This is to make sure your cancer has not come back.
If you have medullary thyroid cancer, other tests are also used to monitor your cancer. Your healthcare provider will give you more information.
