Hormon pg/ml (pmol/l)
Free T3
Active thyroid hormone triiodothyronine
Also known as
fT3 free triiodothyronine FT3
Definition
Free T3 (fT3) is the biologically active form of thyroid hormone and directly regulates metabolism, heart rate, and thermogenesis at cellular receptors. Only the unbound fraction is metabolically active, making it more informative than total T3. A low fT3 despite normal TSH may indicate a conversion problem, for example caused by selenium deficiency.
| Parameter | Value |
|---|---|
| Unit | pg/ml (pmol/l) |
| Reference Range | 2.0–4.4 pg/ml (2.6–5.7 pmol/l) |
| Optimal Range (lab2go) | 3.0–4.2 pg/ml (lab2go Optimum Zone) |
Last Reviewed: 17 April 2026 · maritta