Calculated serum osmolality
Calculate serum osmolality from sodium, glucose and urea, and the osmolal gap if you have a measured value.
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For information only; not a substitute for medical advice. Data is neither sent nor stored.
Formula
Osm = 2 × Na⁺ + glucose + urea (all in mmol/L). Osmolal gap = measured − calculated.
Reference ranges
- 275–295 mOsm/kg
- Osmolal gap: < 10 mOsm/kg
Frequently asked questions
- When is the osmolal gap useful?
- When alcohol poisoning is suspected and the measured osmolality is much higher than the calculated one.