Reverse Triiodothyronine (rT3)
Reverse T3 is the biologically inactive enantiomer of T3 produced when type 3 inner-ring deiodinase (DIO3) removes an iodine atom from the inner ring of T4.
Standard vs. Optimal Reference Rangesng/dL
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
9.2 - 24.1 ng/dL
General reference distribution across unselected commercial populations.
< 15.0 ng/dL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
DIO3 expression is stimulated by systemic inflammation, high cortisol, starvation, and severe physiological stress. rT3 binds TR receptors without activating transcription, acting as a competitive metabolic brake.
Differential Diagnosis
Elevated Levels (rT3 High)
- •Severe chronic physiological or psychological stress
- •Chronic systemic inflammation (high TNF-alpha / IL-6)
- •Caloric deprivation / Anorexia
- •Corticosteroid therapy
Low Levels (rT3 Low)
- •Optimal peripheral deiodination and low physiological stress
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Blood draw must occur strictly between 7:00 AM and 9:00 AM to account for steep circadian cortisol and testosterone peaks. Ensure 8 hours of restful sleep prior; night shift work or sleep deprivation severely blunts endocrine pulsatility. Discontinue biotin supplements for 72 hours before thyroid or steroid testing to prevent false immunoassay results. For reproductive hormones in premenopausal females, precisely document the day of the menstrual cycle (Day 3 for baseline follicular, Day 21 for luteal).
Reflexive Testing Protocol:
- Free Hormone Equilibrium Dialysis or LC-MS/MS assay for direct bioavailable hormone quantification
- Pituitary trophic hormone panel (TSH, LH, FSH, ACTH, Prolactin) to differentiate primary vs central secondary endocrinopathies
- Autoantibody quantification (Thyroid Peroxidase Antibodies, Thyroglobulin Antibodies, 21-Hydroxylase Antibodies)
- Pelvic, testicular, or thyroid high-resolution ultrasound imaging to assess glandular parenchymal architecture
- Dynamic endocrine stimulation testing (Cosyntropin/ACTH stimulation test, Dexamethasone suppression test, GnRH test)
Clinical Citations & Primary Literature (1)
- [1]Deiodinases and the Metabolic Control of Thyroid Action - Nature Reviews Endocrinology (2021). PMID: 34188740
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Reverse Triiodothyronine (rT3) into overall healthspan optimization.