The T3 test measures the level of triiodothyronine (T3), a thyroid hormone that plays a crucial role in regulating metabolism, heart rate, and body temperature. This test is performed by drawing a blood sample, which is then analyzed in a laboratory to determine the amount of T3 in the bloodstream. The T3 test is typically used to diagnose thyroid disorders, such as hyperthyroidism (elevated T3 levels) or hypothyroidism (low T3 levels), and can help assess thyroid function when there are symptoms like unexplained weight loss, rapid heartbeat, or fatigue. It is often administered when thyroid disease is suspected, especially in conjunction with other thyroid tests like T4 and TSH, or for monitoring individuals already receiving treatment for thyroid dysfunction. The test may also be used to evaluate thyroid health in patients with conditions that affect thyroid hormone production.