Convert µIU/mL to ng/dL (and back)
How to convert a value from your report into other units — with the formula and examples.
Formula: there is no general direct formula — it depends on the preparation standard (IU/mg).
How it works
Micro-international units per milliliter measure biological activity, nanograms per deciliter measure mass. There is no universal factor between them: it depends on how many international units 1 mg of the particular preparation contains (and this differs between WHO standards of different years).
Examples for common markers
| Marker | Molar mass / valence | Conversion example |
|---|---|---|
| Prolactin | ~21–23 IU/mg (WHO standard 84/575) | 1 ng/mL ≈ 21–23 µIU/mL |
| hCG | ~6–12 IU/mg (depends on the standard) | 1000 IU/L = 1000 mIU/mL; to get ng/mL, divide by roughly 6–12 |
| FSH, LH, TSH | individual standard | mIU/mL = IU/L (FSH, LH); µIU/mL = mIU/L (TSH) — the numbers are the same |
Bottom line: for hormones it is almost always enough to remember that µIU/mL = mIU/L and mIU/mL = IU/L. Converting to mass (ng/dL) without knowing the standard used in the laboratory's method is inaccurate — check against the reference range on your report.