A T3 test measures the level of triiodothyronine, one of the main hormones produced by the thyroid gland. T3 plays a major role in regulating metabolism, energy levels, body temperature, and overall thyroid function. Elevated T3 levels may indicate hyperthyroidism, while low levels can be seen in hypothyroidism or certain chronic illnesses. Doctors recommend this test when symptoms like weight changes, fatigue, hair loss, anxiety, irregular heartbeat, or temperature intolerance suggest a thyroid imbalance.

For the T3 test, a small blood sample is taken from a vein, and no fasting or special preparation is required. The test is usually performed along with TSH and T4 for a complete thyroid profile. The results help diagnose thyroid disorders, monitor treatment, and evaluate general hormonal health.