rT3

Q: Reverse T3 is an __________ metabolite of thyroxine? (select one)

A) active

B) inactive

Answer: B

Reverse T3 (rT3) is an inactive metabolite of thyroxine. Although it has limited utility in conventional outpatient practice but in ICU it helps in distinguishing central hypothyroidism from nonthyroidal illness.

It is also used in the diagnosis of consumptive hypothyroidism, and MCT8 or SBP2 mutations.

#endocrinology

References:

Schmidt RL, LoPresti JS, McDermott MT, et al. Does Reverse Triiodothyronine Testing Have Clinical Utility? An Analysis of Practice Variation Based on Order Data from a National Reference Laboratory. Thyroid 2018; 28:842.