Osmol gap
In clinical chemistry, the osmol gap is the difference between measured blood serum osmolality and calculated serum osmolality. == Calculation == The osmol gap is typically calculated with the following formula (all values in mmol/L): OG = measured serum osmolality − calculated osmolality = measured serum osmolality − ( 2 × [ Na + ] + [ glucose ] + [ urea ] ) {\displaystyle {\begin{aligned}{\text{OG}}&={\text{measured serum osmolality}}-{\text{calculated osmolality}}\\[4pt]&={\text{measured serum osmolality}}-{\Bigl (}2\times [{\ce {Na^+}}]+[{\ce {glucose}}]+[{\ce {urea}}]{\Bigr )}\end{aligned}}} In non-SI laboratory units: Calculated osmolality = 2 x [Na mmol/L] + [glucose mg/dL] / 18 + [BUN mg/dL] / 2.8 + [ethanol/3.7] (note: the values 18 and 2.8 convert mg/dL into mmol/L; the molecular weight of ethanol is 46, but empiric data shows that it does not act as an ideal osmole in solution and the appropriate divisor is 3.7) A normal osmol gap is < 10 mOsm/kg .