The relationship of methanol and formate concentrations in fatalities where methanol is detected

Abstract

An automated headspace gas chromatography method was developed for the determination of formate (formic acid) in postmortem specimens, based on the in situ sulfuric acid-methanol methylation of formic acid to methyl formate. Diisopropyl ether was used as an internal standard. The method was applied to over 150 postmortem cases where methanol was detected. Of the 153 cases presented, 107 deaths were attributed to acute methanol toxicity. In the vast majority of the remaining 46 deaths, the methanol was determined to be present as a postmortem or perimortem artifact, or was otherwise incidental to the cause of death. Of the 76 victims who were found dead and blood was collected by the medical examiner, all but one had a postmortem blood formate concentration greater than 0.50 g/L (mean 0.85 g/L; n = 74). The sole exception involved suicidal ingestion of methanol where the blood methanol concentration was 7.9 g/L (790 mg/100 mL) and blood formate 0.12 g/L. In 97% (72/74) of the cases where blood was available, the blood formate was between 0.60 and 1.40 g/L. In 31 of the 153 cases, the victim was hospitalized and blood obtained on admission or soon after was analyzed for methanol and formate during the subsequent death investigation; the vast majority (27/30) had antemortem blood formate concentrations greater than 0.50 g/L. Cases with samples taken prior to death with blood formate concentrations less than 0.5 g/L can readily be explained by active treatment such as dialysis. The blood formate method has also been useful in confirming probable perimortem or postmortem contamination of one of more fluids or tissues with methanol (e.g., windshield washer fluid or embalming fluid), where methanol ingestion was unlikely.