Why do some dr's swear by a reverse t-3 test for a valid thyroid diagnoses, but other dr's say "myth, not neccesary". and refuse to order the test.?

Reverse t3 (liothyronine): Doctors are not taught about reverse T3 (liothyronine) in training. Most physicians that know about this test learned about it on their own. This test is important in the proper conversion of T4 to its active form t3 (liothyronine). Reverse T3 (liothyronine) is the mirror image of T3 (liothyronine) and sits on the same receptor site as T3 (liothyronine) but is inactive. You need to look at the entire picture in order to optimize thyroid therapy.