Free T3 Test (FT3)

A Free T3 Test (FT3) measures the level of triiodothyronine, which is the active form of thyroid hormone in the bloodstream that is not bound to proteins. This test is often done in conjunction with other thyroid function tests to help diagnose thyroid disorders, monitor treatment for thyroid diseases, and evaluate metabolism and energy levels. It can also be used to diagnose conditions such as hyperthyroidism and hypothyroidism. A healthcare provider may order a Free T3 Test if a patient is experiencing symptoms of thyroid dysfunction, such as fatigue, weight changes, or changes in heart rate.