Triiodothyronine

Abstract
Triiodothyronine (T3) is normally present in human serum, two thirds being a secretory product of thyroid gland and the remaining one third being derived from extrathyroid conversion of thyroxine to T3. Serum T3determination has become an important factor in the investigation of thyroid physiology and is now available to the clinician in the diagnosis and management of various thyroid disorders. In general, thyrotropinstimulating hormone or thyroxine levels are better diagnostic indexes of hypothyroidism, while T3determination is a useful index of thyroid hyperfunction.