numerical difference between the measured serum osmolality and the serum osmolarity calculated from the clinical chemistry measurements of the serum sodium ion, glucose, and blood urea nitrogen (BUN) concentrations. The normal osmol gap is < 10 mOsm. An elevated osmol gap suggests the presence of an osmotically active substance (methanol, ethanol, ethylene glycol, and isopropanol) in the plasma that is not accounted for by the sodium ion, glucose, or BUN concentration.