Reverse T3, Serum LabCorp

Reverse T3 is a biologically inactive form of T3. Usually, when T4 converts to T3 in the body, a percentage of the T3 is in the form of Reverse T3. When the body is undergoing stress (i.e. a serious illness), thyroid hormone levels may be outside of normal ranges even though there is no thyroid disease present. Reverse T3 may elevate in non-thyroidal conditions, particularly in the stress of illness. It is typically recommended that thyroid testing be avoided in hospitalized patients or deferred until after a person has recovered from acute illness.