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January 21, 1974

Triiodothyronine: Physiological and Clinical Significance

Author Affiliations

From the Mayo Clinic and Mayo Foundation, Rochester, Minn.

JAMA. 1974;227(3):302-304. doi:10.1001/jama.1974.03230160030007

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 T3 determination 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 T3 determination is a useful index of thyroid hyperfunction.