**NOTE: All laboratory testing requires an authorizing physician in order to complete the laboratory testing.**
Reverse T3 is a biologically inactive form of T3. When T4 is converted to T3 in the body, a certain percentage of the T3 is in the form of RT3. When the body is under stress, thyroid hormone levels may be outside of normal ranges even though there is no thyroid disease present. RT3 may be elevated in non-thyroidal conditions, particularly the stress of illness.