Indicator Explainer
Triiodothyronine
A thyroid hormone containing 3 iodine atoms generally synthesized from levothyroxine, and has greater biological activity.
This page explains what the indicator is and how results are interpreted in general terms. Reference ranges depend on the laboratory, the method, and your own situation — no single “normal value” applies to everyone. This page is health information, not a diagnosis. For symptoms, treatment, or urgent concerns, contact a healthcare professional.
When it is tested
Source: National Cancer Institute, NCI Thesaurus 26.09d, C2303. NCI definition, reproduced without modification under CC BY 4.0. Source identity and definition checked automatically on 2026-10-18. No individual clinical interpretation or human reviewer is asserted.
Reading results
Reference intervals and interpretation depend on the laboratory, specimen, method and clinical context. This source definition is educational information; it does not establish a diagnosis, product approval or suitability for an individual.
Also Known As
References
- NCI Thesaurus 26.09d — Triiodothyronine (C2303)
- Source: National Cancer Institute, NCI Thesaurus 26.09d, C2303. NCI definition, reproduced without modification under CC BY 4.0.
- Serum reverse triiodothyronine in dogs with hypothyroidism, nonthyroidal illness syndrome and healthy dogs. — PLoS One, 2026-10-05 (PMID 42832498; literature)
- Non-thyroidal illness syndrome and isolated low triiodothyronine as prognostic markers in acute illness: a systematic review and meta-analysis. — Endocrine, 2026-09-28 (PMID 42804119; literature)
- Free triiodothyronine in intracranial aneurysms: a sex-specific association with unruptured disease and a non-thyroidal illness signal after rupture. — Front Neurol, 2026-09-23 (PMID 42846038; literature)