The Osmolal Gap in Renal Failure

Excerpt

The osmolal gap may be defined as the difference between the calculated and measured serum osmolalities. The calculated component of this entity may be derived from the following formula (1): Serum osmolality (mosmol/kg H₂O) = 1. 86 Na + [glucose/18] + [blood urea nitrogen/2.8] + 9. (In the absence of substantial increases in serum lipids or proteins, mosmol/L and mosmol/kg H₂O may be used interchangeably.)

By using this equation, Dorwart and Chalmers (1) were able to match the calculated and measured serum osmolalities in 715 blood samples drawn from healthy persons. Thus, the constant term, 9 mosmol/kg H₂O, quantitates the