The Reverse T3 (RT3) test measures the inactive form of the hormone T3 or Triiodothyronine.
Triiodothyronine is one of two major hormones produced by the thyroid (the other is T4, or thyroxine). Under normal conditions, the body converts T4 to T3 and RT3 in specific ratios. In certain circumstances, the amount converted to RT3 rises, such as when the body is under stress, as in cases of serious or acute illness or injury. Drugs such as amiodarone and glucocorticoids can also cause increased RT3 levels. RT3 levels alone may not be indicative of a thyroid condition, since stress can cause levels to rise. A more accurate assessment may be gained by combining the Reverse T3 Test with the Free T3 Test to evaluate the ratio between RT3 and free T3 levels.
Production of Reverse T3 is typically triggered when the body is under significant stress. Conditions which can lead to RT3 production include but are not limited to:
- periods of prolonged stress
- extreme dieting
- insulin dependent diabetes
- exposure to certain chemicals or toxic metals
- liver or kidney disease
- serious injury
- chronic alcohol ingestion
- abnormally low levels of certain nutrients