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' - 'standard' T3 is the active thyroid hormone that stimulates the body's energy system (metabolism). Reverse T3 is a mirror image - it goes into cells, and instead of controlling metabolic processes 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 - so normal thyroid levels with high reverse T3 may still result in hypothyroidism.
Thyroid function test: diagnose hypothyroidism or hyperthyroidism in conjunction with T4 result. Acute or chronic stress or illness favors the formation of RT3 (rather than T3): whereas, T4 concentrations remain essentially unchanged.