What is the Best Formula for Predicting Osmolar Gap?

Serum osmolarity can be calculated using the concentrations of the major constituents of serum namely sodium, potassium, glucose and urea. The osmolar gap is defined as the difference between the measured osmolality and calculated osmolarity. An osmolar gap is due to the presence of low molecular weight, osmotically active solutes, which are not included in the calculated osmolarity. For example, osmolar gap calculation may be used as a rapid screening procedure in the diagnosis of ethanol poisoning. 1 Sick cell syndrome is characterized by an osmolar gap.2 It is therefore beneficial to have a reliable estimate of osmolar gaps. Many formulae have been suggested for osmolar gap calculation. This study was designated to investigate the utility of the published formulae in surgical outpatients (SOPO) and in severely ill patients in an intensive therapy unit (lTU).