The osmolar gap is used to identify unmeasured compounds in serum or plasma when present in high molar concentrations. If the plasma ethanol concentration is available, please use “serum osmolar gap (including ethanol) calculator”. The equation is based on the difference between measured osmolality and calculated osmolality.
Serum osmolar gap = measured osmolality – 2 x Sodium – urea – glucose (all results in mmol/L except measured osmolality in mmol/kg)
Serum Osmolar Gap reference interval is 0 to +10 mmol/L Interpretation A raised osmolar gap may be caused by high concentrations of ethanol, methanol, ethylene glycol, mannitol or glycine. The osmolar gap may also be high in pseudohyponatraemia caused by very higher serum lipids or serum protein.