Hormon ng/dl (pmol/l)
Free T4
Thyroid prohormone thyroxine
Also known as
fT4 free thyroxine FT4
Definition
Free T4 (fT4, free thyroxine) is the primary secretory product of the thyroid gland and acts as a prohormone, converted to biologically active T3 in peripheral tissues (liver, kidney, muscle) through deiodination. The combination of TSH and fT4 allows differentiation between primary and secondary thyroid disorders. Reference values vary by assay method and laboratory.
| Parameter | Value |
|---|---|
| Unit | ng/dl (pmol/l) |
| Reference Range | 0.7–1.9 ng/dl (9.0–24.5 pmol/l) |
| Optimal Range (lab2go) | 1.0–1.7 ng/dl (lab2go Optimum Zone) |
Last Reviewed: 17 April 2026 · maritta