Individual test · Labcorp 010389

Triiodothyronine (T3), Free

This test measures the amount of free triiodothyronine (T3) in your blood, which is the active form of a thyroid hormone that is not attached to proteins. It helps show how well your thyroid is regulating your body's energy and metabolism, particularly if you have symptoms like rapid heartbeat or unexplained weight loss. Doctors use this measurement to help identify or rule out an overactive thyroid gland, also known as hyperthyroidism. However, this test alone cannot determine the specific underlying cause of a thyroid condition without further evaluation.