Use

Reverse triiodothyronine (rT3) is an isomer of triiodothyronine (T3) with no demonstrated biological activity. The majority of rT3 is produced through peripheral enzymatic monodeiodination of T4 at the 5 position of the inner ring of the iodothyronine nucleus of thyroxine (T4). A lesser amount is secreted directly by the thyroid gland. rT3 is biologically inactive and does not stimulate thyroid hormone receptors. In nonthyroidal illness syndrome, rT3 levels increase while T3 levels decrease, seen in acute or chronic systemic nonthyroidal illnesses. An elevated rT3 level can independently predict increased mortality in acutely ill patients.