Free T3 and Reverse T3

Free Triiodothyronine (Free T3 or FT3) is the active form of thyroid hormone in our body - this is the actual hormone that does the work at the cellular level. Although not always needed for monitoring thyroid treatment regimes, many specialists advise testing the level of FT3 particularly if the treatment regime is less conventional.

Reverse T3 may be raised at times of acute or chronic stress or illness and it is suggested its presence may interfere with the action of Free T3 on the body. There is controversy about the role of Reverse T3 in thyroid illness. Conventional endocrinologists (hormone specialists) generally believe that knowledge of the level of this substance does not influence thyroid treatment decisions. The alternative view however is that Reverse T3 is effectively 'antithyroid'. Free T3 is the active thyroid hormone that stimulates the body's energy system (metabolism). Reverse T3 is a mirror image - it is taken up by cells, and when incorporated it blocks the effect of T3. In this model, Reverse T3 is effectively a hibernation hormone - in times of stress and chronic illness it lowers energy release from the cells. In this scenario, a normal thyroxine level measured when Reverse T3 is high may mask hypothyroidism.

Please be aware that Reverse T3 samples are sent to the USA for analysis so turnaround time is prolonged.