Osmolal gap calculator

Osmolal Gap

Serum Osmolal Gap

Parameter	Value
Measured Serum Osmolality (mOsm/kg)
Sodium (Na⁺) mEq/L
BUN (mg/dL)
Glucose (mg/dL)
Results
Calculated Osmolality	mOsm/kg
Osmolal Gap	mOsm/kg

Interpretation
<10	Normal — No significant unmeasured osmoles detected.
>10	Elevated — Consider toxic alcohol ingestion: methanol, ethylene glycol, isopropanol, or other unmeasured osmoles (ethanol, mannitol, contrast dye).

References
Smithline N, Gardner KD Jr. Gaps—anionic and osmolal. JAMA. 1976;236(14):1594-1597. PMID 989116. Kraut JA, Xing SX. Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis. Am J Kidney Dis. 2011;58(3):480-484. PMID 21794966. Formula: Calculated Osm = 2(Na) + BUN/2.8 + Glucose/18. Gap = Measured − Calculated.