Osmolal and anion gaps in patients admitted to an emergency medical department

Abstract

1. Osmolal and anion gaps are helpful in the diagnosis and evaluation of intoxications with methanol and ethylene glycol. Reported reference values for osmolal gap and anion gap are -1 (+/- 6) mosm kg-1 H2O and 16 (+/- 2) mmol l-1, respectively. However, we have repeatedly found unexplained increased gaps in patients admitted to our department, and the relevance of the established reference values has been questioned. 2. Osmolal and anion gaps were determined in an unselected population of patients consecutively admitted to an emergency medical department. In the case of unexplained gaps, the blood samples were analysed with respect to the presence of alcohols and organic acids. 3. We included all accessible patients admitted during 14 days. Appropriate blood samples were obtained in 177 patients (88 male, 89 female), with a mean age of 65 years (range 17-94). 4. The mean and (standard deviation) for osmolal and anion gaps in our material were 5.2 mosm kg-1 H2O (7.0) and 12.9 mmol/l (4.2). Neither methanol nor ethylene-glycol was detected in serum from any patients. Small amounts of ethanol were found in 5 patients, and high lactate levels explained in part the most extensively increased anion gaps. However, the calculated analytical standard deviation accounted entirely for the variation in our material, and we suggest that the present reference values be adjusted.