Serum osmolality calculator

Calculated Serum Osmolality

Calculated Serum Osmolality

Parameter	Value
Sodium (mEq/L)
BUN (mg/dL)
Glucose (mg/dL)
Calculated Osm	mOsm/kg

Interpretation

275–295	Normal serum osmolality.
Osmolal gap = Measured Osm – Calculated Osm. Gap >10 suggests unmeasured osmoles (toxic alcohols, mannitol, etc.).

References

Formula: Osm = 2×Na + BUN/2.8 + Glucose/18 Purssell RA, et al. Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap. Ann Emerg Med. 2001;38(6):653-659. PMID 11719745.