Synonyms:

• Reverse Tri-iodothyronine
• T₃, Reverse

Reverse T₃ measurement may be useful in evaluating the euthyroid sick patient with low T₃ concentrations. Also useful in evaluating thyroid function and metabolism. Not to be confused with tri-iodothyronine.

Reverse T₃ is derived almost completely from the peripheral monodeiodonization of thyroxine and has minimal physiological activity. T₃ concentrations are elevated in acute or chronic diseases due to changes in peripheral rates of conversion of T₄ to T₃ and reverse T₃. Several drugs such as glucocorticoids and amiodarone cause increased levels of reverse T₃. Reverse T₃ levels are elevated at birth and decline to normal levels by the first week of life. Measurement of reverse T₃ may be of use in assessing thyroid function and metabolism in the newborn.