Thyroid Function Tests
What are thyroid function tests?
Thyroid function tests (TFTs) are a group of tests that are requested together to help evaluate thyroid gland function and to help diagnose thyroid gland disorders. TFTs include a measure of the amount of thyroid hormones, Thyroxine (T4) or Tri-iodothyronine (T3) in your blood. These hormones are chemical substances that travel through the bloodstream and control or regulate your body’s metabolism—how it functions and uses energy. Thyroid hormones are present in the blood in either protein bound forms (the majority) or the free and active form of the hormone. Currently, the majority of UK laboratories measure the free form of the hormones – Free T4 (FT4) or Free T3 (FT3).
Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland and is part of the body’s feedback system to maintain stable amounts of thyroid hormones in the blood. When thyroid hormone concentrations decrease in the blood, the pituitary gland is stimulated to release TSH, which in turn stimulates the production and release of T4 and T3 by the thyroid gland. When the system is functioning normally, TSH production turns on and off to maintain constant blood thyroid hormone concentrations.
Thyroid Function Tests usually include some combination of:
- TSH (thyroid stimulating hormone or thyrotropin)– to test for hypothyroidism, hyperthyroidism and to monitor thyroid replacement therapy
- T4 or FT4– to test for hypothyroidism and hyperthyroidism
- T3 or FT3– to test for hyperthyroidism
Why Get Tested?
To help evaluate thyroid gland function and to help diagnose thyroid disorders
When to Get Tested?
As part of a health checkup or when symptoms suggest hypo- or hyperthyroidism due to a condition affecting the thyroid
Sample Required?
A blood saple taken from a vein in your arm
Test Preparation Needed?
None needed; however, certain medications can interfere with the tests included in the panel, so tell your doctor about any drugs that you are taking.
