The Total T4 test measures the complete amount of T4, your thyroid's main 'storage' hormone, in your bloodstream (both 'bound' and 'free'). It's a foundational test that provides a broad look at your thyroid's total output. It's used to help screen for hypothyroidism (low T4) and hyperthyroidism (high T4). A simple blood draw is required. For a more precise, modern assessment, we recommend our Free T4 test, which measures only the active, usable hormone. This is a standard part of our Thyroid Function Profile.