The reverse T3 test measures the amount of reverse T3, a thyroid hormone, in your blood. High levels of reverse T3 can indicate that the body is under stress.

Reverse T3 (rT3) is an inactive thyroid hormone isomer that serves as a natural regulatory mechanism in the body’s metabolic processes.

Key Characteristics: • Inactive form of triiodothyronine • Produced from T4 hormone • Comprises 0.9% of thyroid hormones released • 95% produced outside the thyroid gland

Clinical Significance: • Natural metabolic “buffer” against hyperthyroidism • Competes with active T3 for cellular receptor sites • Can block thyroid hormone effects

Production Mechanisms: • Converted by deiodinase enzymes • Removes iodine atom from T4 molecule • Produced during: • Chronic illness • Extreme stress • Starvation • Critical medical conditions

Important Considerations: • Elevated levels may indicate metabolic adaptation • Can cause hypothyroidism-like symptoms • Not routinely measured in standard thyroid panels

Reverse T3 represents a sophisticated metabolic regulatory mechanism that helps protect the body from excessive thyroid hormone activity.