Reverse T3
Also written as: rT3 — Reverse T3
An inactive thyroid hormone metabolite that can indicate non-thyroidal illness or thyroid hormone resistance.
Full Definition
Reverse T3 (rT3) is an inactive metabolite of thyroxine (T4) formed by the enzyme type 3 deiodinase, which removes an iodine atom from the inner ring of T4. Unlike the active hormone T3, reverse T3 has no significant biological activity and serves as a mechanism for reducing thyroid hormone action during illness or stress. Elevated rT3 levels may be seen in non-thyroidal illness syndrome, certain medications, and thyroid hormone resistance. rT3 testing is not routinely recommended but may be useful in specific clinical scenarios.
Usage
Usage note: Lowercase 'r' in rT3; distinguish clearly from T3 (triiodothyronine).
In Context
- "Elevated reverse T3 levels were consistent with non-thyroidal illness syndrome in the critically ill patient." — Critical care consultation
- "The rT3 to T3 ratio was calculated to assess peripheral thyroid hormone conversion." — Thyroid function evaluation