The Free Triiodothyronine (FT3) test is used to measure the levels of the free and active form of the thyroid hormone triiodothyronine in the blood. FT3 is one of the main hormones produced by the thyroid gland and plays a crucial role in regulating metabolism, energy, and growth. This test is performed to evaluate thyroid function, especially in cases where symptoms such as fatigue, unexplained weight loss, or weight gain are present. The test helps in diagnosing thyroid disorders such as hyperthyroidism or hypothyroidism, contributing to appropriate treatment guidance and improving patient healthcare.