Anion and Osmolal Gaps in the Diagnosis of Methanol and Ethylene Glycol Poisoning

Abstract

The diagnostic value of determination of the anion and osmolal gaps was studied in 6 patients poisoned with methanol and in 5 poisoned with ethylene glycol. Increased osmolal gap was present on admission in all patients; increased anion gap was present in all except one. In methanol-poisoned patients the mean blood values as follows: pH 7.27, anion gap 24 mmol/l, osmolal gap 81 mosmole/kg H2O, methanol 67 mmol/l, ethanol 11 mmol/l; in the ethylene glycol-poisoned patients values were: pH 6.93, anion gap 38 mmol/l, osmolal gap 35 mosmole/kg H2O and ethylene glycol 24 mmol/l. In the absence of alcoholic acidosis or diabetic coma, the finding of a simultaneous increase in the anion and osmolal gaps indicated methanol or ethylene glycol poisoning. Determinations of the anion and osmolal gaps are mandatory whenever facing metabolic acidosis of unknown etiology.