All answers
Answer · hormone optimization
Free T3 vs total T3 — which is more useful?
Short answer
Free T3 reflects unbound, biologically active hormone and is preferred in most thyroid evaluations. Total T3 is informative when binding proteins are altered.
Reviewed by Dr. Laura PurdyMay 29, 2026
Full answer
Free T3 is the unbound, biologically active fraction of triiodothyronine and is preferred for most thyroid evaluation. Total T3 measures both bound and free hormone and is affected by binding protein concentrations — pregnancy, oral estrogen, nephrotic syndrome, and protein-binding disorders all shift total T3 without changing free T3. Within oMeds review, free T3 is the default; total T3 is reviewed when binding protein status materially alters interpretation.
Educational. Not a substitute for individualized provider review.
References & sources
- Free T3 — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29
Primary source
Free T3