Question: what is the difference between free t3 and t3?
Answer: Total T3 is the total amount of triiodothyronine circulating in the blood, both bound and unbound by protein. 1﻿ Free T3 is not bound to protein and considered the active form of triiodothyronine. Reverse T3 is the inactive "mirror image" of T3 that attaches to thyroid receptors but is unable to activate them.