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March 6, 1996

Is Triiodothyronine Administration Beneficial in Patients Undergoing Coronary Artery Bypass Surgery?

Author Affiliations

From the Endocrinology Division, Washington Hospital Center, and the Endocrine Division, George Washington University Medical Center, Washington, DC.

JAMA. 1996;275(9):723-724. doi:10.1001/jama.1996.03530330067033

There have been significant advances in our understanding of thyroid pathophysiology as well as in our ability to measure thyroid-stimulating hormone (TSH), total and free triiodotriiodo- (T3), and thyroxine (T4).1 The thyroid gland normally produces approximately 90 μg of T4 and 40 μg of T3 daily; all of circulating T4 is derived from direct thyroidal secretion, whereas about 85% of T3 comes from extra thyroidal conversion of T4 to T3, with only about 15% of T3 being produced by direct thyroidal secretion. Over 99% of circulating T4 and T3 are bound to serum-binding proteins, and it is only the small unbound fraction that is biologically active. Thyroxine is mainly a prohormone, and T3 is responsible for most if not all of the biological activity attributable to thyroid hormone. In many clinical situations, including systemic illness, surgery, and