⚕️ For clinical reference only. Not a substitute for professional judgment.

Osmolal Gap Toxicology

Difference between measured and calculated osmolality. Gap >10 mOsm/kg suggests toxic alcohols, ethanol, or other unmeasured osmoles.

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Enter lab values

Enter measured osmolality and serum values to calculate osmolal gap.

Laboratory Values

Measured Osmolality

mOsm/kg

Sodium

mmol/L

Glucose

mmol/L

Urea

mmol/L

Formula

Calculated Osm = 2xNa + Glucose + Urea (mmol/L) Osmolal Gap = Measured - Calculated Normal: <10 mOsm/kg Elevated (>10): ethanol, methanol, ethylene glycol, isopropanol, propylene glycol, mannitol

When to use

Suspected toxic alcohol ingestion — methanol or ethylene glycol
HAGMA with unexplained elevation — calculate alongside anion gap
Ethanol: gap of ~21 per 100 mg/dL blood alcohol level
Large gap (>25) + HAGMA = toxic alcohol until proven otherwise