Individual test · Labcorp 001149

Thyroxine (T4)

This test measures the total amount of thyroxine (T4), a hormone produced by your thyroid gland that controls how your body uses energy. It helps show whether your thyroid is overactive or underactive, which is often checked when patients experience fatigue or unexplained weight changes. While this measurement helps screen for thyroid disorders, it cannot diagnose a specific condition on its own because protein levels, medications, and other illnesses can also affect T4 levels.