Also known as: Reverse Tri-iodothyronine, T3, Reverse.

T3 concentrations are elevated in chronic or acute diseases because of changes in peripheral rates of conversion of T4 to T3 and reverse T3. Drugs such as amiodarone and glucocorticoids cause increased levels of reverse T3. Reverse T3 levels are elevated at birth and will decline to normal levels by the first week of life. Measurement of reverse T3 may be of use in the assessment of thyroid function and metabolism in the newborn.