Calculated osmolality & osmolar gap

Calculated serum osmolality (2 × Na + glucose + urea, SI units) and the gap against a measured value.

Sodium(mmol/L)Glucose(mmol/L)Urea(mmol/L)Measured osmolality (optional)(mOsm/kg)

Result

Fill the inputs to compute.

Interpretation: The gap screens for unmeasured osmoles, classically toxic alcohol ingestions.
Limitations: A normal gap late in a toxic alcohol course does not exclude ingestion: the parent alcohol is metabolized to anions that raise the anion gap instead.
Reference: Purssell RA et al. Osmole gap review. J Emerg Med 2004;27:343-6.

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