Thyroid Function Tests (TFTs)

This information describes thyroid function tests (TFTs).

Thyroid function tests are blood tests that let your doctor see if you have the right amount of thyroid hormone in your blood.

Thyroid Stimulating Hormone (TSH)

Thyroid stimulating hormone (TSH) is made and released by the pituitary gland in your brain. It stimulates your thyroid to work.

The level of TSH in your blood tells us if your thyroid is too active or not active enough. If you don’t have a thyroid due to surgery, your TSH level tells your doctor if you’re getting the right dose of thyroid hormone replacement medication.

The normal TSH range differs slightly from one lab to another. At Memorial Sloan Kettering MSK), the normal range is 0.55  milli-international units per liter (mIU/L) to 4.78 mIU/L.

  • If your TSH level is low, you’re in a state of hyperthyroidism. That means your thyroid function is too active.
  • If your TSH level is high, you’re in a state of hypothyroidism. That 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 most people with thyroid cancer, the goal is to keep their TSH level below the normal range for the first couple of years after being diagnosed. This may lower the risk of the cancer coming back. Your doctor will tell you what level is right for you,

 

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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 0.9 nanograms per deciliter (ng/dL) to 1.8 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 goal is to keep their FT4 level near the upper limits of the normal range.
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Thyroglobulin

Thyroglobulin is a protein in the blood that’s produced only by 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 to be sure your cancer hasn’t returned.

If you have medullary thyroid cancer, other tests are also used to monitor your cancer. Your doctor or nurse will give you more information.

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