Osmolal Gap calculator
Result
5mOsm/kg
Normal (≤10)
Calculated osmolality: 290 mOsm/kg.
How to use it
- 1
Simultaneous blood samples. Na, glucose, urea from same draw as measured osmolality.
- 2
Formula. Calculated = 2×Na + Glucose + Urea (all mmol/L).
- 3
Gap > 10 mOsm/kg. Consider ethanol (most common), methanol, ethylene glycol, isopropanol, mannitol.
When to use it
- Suspected toxic ingestion
- Methanol and ethylene glycol both cause HAGMA + osmolal gap.
- Undifferentiated HAGMA
- HAGMA + osmolal gap + visual symptoms → methanol.
- Ethanol known
- Subtract ethanol contribution (BAL mg/dL ÷ 4.6 ≈ osmolar contribution).
A reference for clinicians and students, not medical advice. A score supports a decision; it does not make one. Check every result against the patient in front of you and your local protocol.
At a glance
- Specialty
- Nephrology
- Inputs
- 4
- Type
- Formula
