The Total T3 (Tri-iodothyronine) test measures the level of T3 hormone in the blood, which is essential for metabolism and energy regulation. It aids in diagnosing thyroid disorders like hyperthyroidism and hypothyroidism. Elevated T3 levels may indicate hyperthyroidism, while low levels can suggest hypothyroidism or chronic illness. This test is commonly used alongside T4 and TSH tests for a comprehensive thyroid function assessment.