{"id":"reverse-t3","name":"Reverse T3","shortName":"Reverse T3","aliases":["rT3","T3, Reverse","Reverse Triiodothyronine","Reverse T3, LC/MS/MS","RT3","T3 Reverse","T3 Reverse, LC/MS/MS","T3, Reverse, LC/MS/MS","Reverse T3, Serum","3,3',5'-Triiodothyronine","Triiodothyronine, Reverse","Reverse T3 (rT3)"],"abbreviations":["rT3","RT3"],"loinc":[{"code":"3052-8","primary":true},{"code":"14929-4","primary":false}],"specimen":"serum-or-plasma","units":[{"ucum":"ng/dL","display":"ng/dL"},{"ucum":"nmol/L","display":"nmol/L"},{"ucum":"pmol/L","display":"pmol/L"},{"ucum":"pg/mL","display":"pg/mL"},{"ucum":"ng/L","display":"ng/L"}],"referenceRanges":[{"population":"Adults","low":8,"high":25,"unit":"ng/dL","unitDisplay":"ng/dL","note":"Quest Diagnostics' interval for its LC-MS/MS method, as listed in the Mayo-hosted test catalog; the page gives no age or sex limits. Intervals depend on the method. A radioimmunoassay used in a Norwegian trial lists 0.14 to 0.54 nmol/L (about 9 to 35 ng/dL) for women. In healthy volunteers measured by LC-MS/MS, evening samples ran higher than morning ones. Reverse T3 is rarely useful in routine care according to the ATA-commissioned 2023 review. Mass-spectrometry methods have largely replaced radioimmunoassay, and the 2024 European Thyroid Association guideline lists a low reverse T3 as part of the profile of MCT8 deficiency, a rare inherited condition. Use the interval printed on your own report.","sources":[{"title":"T3 Reverse, LC/MS/MS (Quest Diagnostics test FRT3S)","url":"https://www.testcatalog.org/show/FRT3S","publisher":"Quest Diagnostics Nichols Institute, via the Mayo Clinic Laboratories extended catalog"},{"title":"Thyroid Signaling Biomarkers in Female Symptomatic Hypothyroid Patients on Liothyronine versus Levothyroxine Monotherapy: A Randomized Crossover Trial","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC9095395/","publisher":"Journal of Thyroid Research","year":2022},{"title":"Demonstration of reciprocal diurnal variation in human serum T3 and rT3 concentration demonstrated by mass spectrometric analysis and establishment of thyroid hormone reference intervals","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC7257839/","publisher":"Therapeutic Advances in Endocrinology and Metabolism","year":2020},{"title":"Thyroid Stimulating Hormone and Thyroid Hormones (Triiodothyronine and Thyroxine): An American Thyroid Association-Commissioned Review of Current Clinical and Laboratory Status","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC10517335/","publisher":"Thyroid (American Thyroid Association)","year":2023},{"title":"Clinical and laboratory aspects of 3,3',5'-triiodothyronine (reverse T3)","url":"https://pubmed.ncbi.nlm.nih.gov/33040575/","publisher":"Annals of Clinical Biochemistry","year":2021},{"title":"2024 European Thyroid Association Guidelines on diagnosis and management of genetic disorders of thyroid hormone transport, metabolism and action","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC11301568/","publisher":"European Thyroid Journal","year":2024}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"An inactive by-product of thyroxine (T4). Its usefulness is limited, and an American Thyroid Association review says routine testing is not needed.","url":"https://bloodtesttracker.com/markers/reverse-t3","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}