Analysis of serum anion gap and osmolal gap in diagnosis and prognosis of acute methanol poisoning: clinical study in 86 patients

Abstract

We performed a retrospective study in 86 patients from the Czech methanol outbreak in 2012 to determine the role of anion and osmolal gaps in diagnosis and prognosis of methanol poisoning. Methanol and ethanol were measured by a gas chromatographic method with flame ionization detection. Formate was measured enzymatically. Osmolality was measured by freezing point depression method. From 86 patients, 15 died, 47 survived without, and 24 survived with visual/CNS sequelae. There was a statistically significant correlation between the osmolal gap and serum methanol concentrations (R 2 = 0.704; p < 0.001); however, the sensitivity was low for the detection of serum methanol under 20 mmol dm−3. The survivors without sequelae had lower osmolal gap than those who survived with visual/CNS damage (p = 0.002). The correlation between the anion gap and serum formate on admission was significant (R 2 = 0.28; p 0.05). The measurement of the serum anion and osmolal gaps is a useful laboratory method of early diagnosis of acute methanol poisoning. Anion gap is a reliable indicator of the severity of poisoning in the late-presenting patients. Increased osmolal gap helps in diagnosing methanol poisoning at an early stage before the results of gas chromatography measurement are available.