Triiodothyronine, Total (Total T3) Unit Converter

Total T3 measures the combined amount of both protein-bound and free (unbound) triiodothyronine in your blood. T3 is the most biologically active thyroid hormone, acting directly on cells throughout the body to regulate metabolism.

About 99.7% of circulating T3 is bound to transport proteins, mainly thyroxine-binding globulin (TBG), with only ~0.3% circulating as the free, active form. Because Total T3 includes both fractions, it can be influenced by changes in binding protein levels from pregnancy, estrogen use, or liver disease.

T3 is roughly 10 times more potent than T4 (thyroxine) at thyroid hormone receptors. It works alongside TSH and Free T4 to give a complete picture of thyroid function.

Only about 20% of circulating T3 is produced directly by the thyroid gland. The remaining ~80% is converted from T4 (thyroxine) in peripheral tissues, primarily the liver and kidneys, by selenium-dependent deiodinase enzymes.