Laboratory

Osmolar Gap

Name: Osmolar Gap | StudyPrometric Tools
Keywords: osmolar gap, toxicology, alcohol, methanol, ethylene glycol, osmolality

Calculates the difference between measured and calculated osmolality.

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Parameters

Osmolar Gap Result

Formula

Calculated Osm = (2 × Na) + (Glucose / 18) + (BUN / 2.8) + (Ethanol / 4.6)
Osmolar Gap = Measured Osmolality - Calculated Osmolality

Clinical Pearls

An elevated osmolar gap (>10) in the setting of an unexplained high anion gap metabolic acidosis is the classic presentation of methanol or ethylene glycol poisoning.

Limitations

A normal osmolar gap does NOT rule out toxic alcohol ingestion, especially if presentation is delayed (as the parent alcohol is already metabolized into toxic acids).