This isolation Reverse T3 (RT3) test measures the inactive form of the hormone T3, or Triiodothyronine. Normally, the body converts T4 into both T3 and RT3 in specific ratios. Elevated RT3 levels are often found in individuals with hypothyroidism. Measuring reverse T3 can help differentiate between thyroid-related conditions and non-thyroidal illnesses. This test is typically used when results from other thyroid tests—such as total T3, total T4, free T4, and TSH—are within expected ranges, but further investigation is needed. Fasting is not required for this test.

After order completion, a provider will submit your Lab Requisition Form to Labcorp, within 24 (business) hours. You will also be emailed a copy of your LRF to take to your nearest Labcorp with valid photo ID. Your results will be available in your Labcorp Patient Portal as soon as they become available, and we will securely email you a PDF copy. Email verification will be required, please check your spam folder.