The FT3 (Free Triiodothyronine) test measures the level of free T3, the active form of the thyroid hormone triiodothyronine that circulates unbound in the blood. T3 is primarily produced by the conversion of thyroxine (T4) in the tissues and plays a vital role in regulating metabolism, heart rate, body temperature, muscle control, and brain development.
This test is used to evaluate thyroid gland function and helps diagnose hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), and monitor thyroid hormone replacement therapy. It is often ordered alongside TSH and FT4 tests to get a complete picture of thyroid function. FT3 is particularly useful in diagnosing T3 toxicosis, a condition where T3 is elevated while T4 remains normal.
