This test measures the level of the active thyroid hormone T3 which is free (not bound to protein) and therefore available to your cells to regulate metabolism.
This test includes (expand individual tests for details):
Triiodothyronine (T3) is one of two major hormones produced by the thyroid gland (the other is called Thyroxine(T4)). This test can tell whether the thyroid is performing properly. Thyroid hormones help regulate the your metabolism (how the body functions).