The Total T4 (Thyroxine) test measures the level of thyroxine, a key thyroid hormone, in the blood. T4 is crucial for regulating metabolism, energy levels, and growth. This test assists in diagnosing thyroid disorders, with elevated T4 levels potentially indicating hyperthyroidism and low levels suggesting hypothyroidism. It is often evaluated alongside T3 and TSH tests for a complete thyroid function profile.