Elevated circulating reverse T3 concentration

What it means

Concentration of reverse T3 (3,3',5'-triiodothyronine or rT3) in the blood circulation is above the upper limit of normal.

Reverse T3 is the third most abundant iodothyronine circulating in human blood and is produced by the inner ring deiodination of the pro-hormone thyroxine (T4). The number 4 in T4 means it has 4 iodine atoms. It can lose 1 of them, yielding either T3 or reverse T3, depending on which iodine atom it loses. Loss of iodine from the five-prime position on its outer ring yields T3, the most potent thyroid hormone. On the other hand, when T4 loses an iodine atom from the five position on its inner ring it yields reverse T3. Reverse T3 is inactive.

Rare diseases that can present with this1

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Elevated circulating reverse triiodothyronine concentration · Elevated rT3