The conversion of T4 to T3 occurs primarily in peripheral tissues and involves deiodinase enzymes, with receptors for T3 found throughout the body.

“but I want to see if somebody's shunting their t4 to reverse t3 which is an inactive form of t3 what I want to see is somebody converting and everyone has a little different ratio but there are generally established ratios for how much t4 to t3 someone should have but you want to see this t4 getting converted to 3 3 and as as you're saying the t3 is really the active hormone this is what binds in the peripheral tissues”

“generally that the thyroid gland makes mostly t4 and then in the peripheral tissues t4 is converted to t3”

“now I just said that basically most of what comes out of the thyroid is T4 which is inactive now it's not entirely clear what the ratio is between these but it's directionally about four or five to one I think it's almost just as easy to imagine that virtually everything the thyroid is producing is T4 so if the thyroid is producing T4 which is inactive it needs to be converted into an active hormone in the body and that's where these enzymes called D iodinases come in”

“and as their name suggests D iodinases remove one of the iodines from T4 to create T3 which is the active hormone”