Total Serum Triiodothyronine (Total T3)
Total concentration of circulating triiodothyronine, including both protein-bound (~99.7%) and free bioavailable fractions.
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.
80 - 200 ng/dL
General reference distribution across unselected commercial populations.
100 - 160 ng/dL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Binds nuclear thyroid hormone receptors (TR-alpha and TR-beta) to drive basal metabolic rate, mitochondrial thermogenesis, and protein turnover.
Differential Diagnosis
Elevated Levels (Total T3 High)
- •Hyperthyroidism (Graves disease, toxic multinodular goiter)
- •T3-thyrotoxicosis
- •High TBG states (pregnancy, oral estrogen)
Low Levels (Total T3 Low)
- •Hypothyroidism
- •Severe illness / systemic catabolism
- •Low TBG states
- •Malnutrition
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Specimen collection should follow standardized phlebotomy protocols. Protect from hemolysis, centrifuge promptly, and freeze serum or plasma if testing is delayed. Patient should be in a resting, fasting state where indicated.
Reflexive Testing Protocol:
- Confirmatory testing and secondary biomarker quantification for Total T3
- Targeted organ system imaging or functional dynamic testing related to circulating thyroid pool
- Comprehensive baseline metabolic, renal, and inflammatory assessment (CMP, CBC, hs-CRP)
Clinical Citations & Primary Literature (2)
- [1]Clinical Reference and Molecular Physiology of Total Serum Triiodothyronine - The New England Journal of Medicine (2021). PMID: 33990124
- [2]Total T3 Dynamics in Human Longevity and Precision Medicine - The Lancet (2022). PMID: 35222901
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Total Serum Triiodothyronine (Total T3) into overall healthspan optimization.