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Calculated osmolality and osmolar gap

Acid-base & electrolytes

An osmolar gap above 10 means something unmeasured is in the plasma: methanol, ethylene glycol, ethanol, mannitol.

What you enter

  • Sodium (mmol/L)
  • Glucose (mmol/L or mg/dL)
  • Urea (mmol/L or mg/dL BUN)
  • Measured osmolality (mOsm/kg)
FORMULACalculated osmolality = 2 × Na + glucose (mmol/L) + urea (mmol/L); gap = measured − calculated
SourceKraut JA, Kurtz I. Toxic alcohol ingestions: clinical features, diagnosis, and management. Clin J Am Soc Nephrol 2008;3:208-25ReviewedFormula and thresholds checked against the source on 2026-08-22. If the source updates, this line will say so.