Reverse T3, Serum

Reverse T3, Serum: Reverse T3 is a form of the thyroid hormone T3 that is inactive. Your body makes it from T4, but instead of boosting energy and metabolism like active T3, reverse T3 helps slow things down when your body is under stress, illness, or low-calorie intake. Normal levels mean your thyroid is balancing active and inactive hormone appropriately. High Reverse T3 can block the action of active T3, leading to symptoms of low thyroid (fatigue, weight gain, brain fog, cold intolerance) even if other thyroid numbers look normal. Low Reverse T3 is usually not a concern.