This test measures the level of triiodothyronine (T3) in your blood. T3 is one of two major

hormones made by your thyroid, a small, butterfly-shaped gland located near the throat. The

other hormone is called thyroxine (T4.) T3 and T4 work together to regulate how your body

uses energy. These hormones also play an important role in controlling your weight, body

temperature, muscle strength, and nervous system.

A T3 test is most often used to diagnose hyperthyrodisim, a condition in which the body

makes too much thyroid hormone.