Interpretation of low postmortem concentrations of ethanol

The interpretation of postmortem blood ethanol concentrations (BAC), especially those less than 0.05 g/dL can be complicated by postmortem ethanol formation. One method used by the toxicologist to respond to this possibility is to analyze multiple specimens for ethanol. Two useful specimens to analyze are vitreous humor and urine, because they are less susceptible to the putrefaction process. A negative vitreous humor and/or urine ethanol would suggest that the measured ethanol resulted from postmortem formation. Data were collected from the Office of the Chief Medical Examiner, State of Maryland and the Armed Forces Institute of Pathology on blood specimens with ethanol concentrations less than 0.05 g/dL to develop a reasonable threshold for interpretation in the absence of other specimens. A total of 381 cases with a BAC between 0.01 and 0.04 g/dL were studied over a 2 year period. Urine and vitreous humor specimens were tested where available. At a BAC of 0.01 g/dL, 54% of the cases were associated with a positive vitreous humor and/or urine ethanol concentration. This percentage increased to 63% when BAC equals 0.02 g/dL. Seventy-three percent and 92% of the cases had a positive alternate specimen if the BAC was 0.03 g/dL and 0.04 g/dL, respectively. In addition, 90% of the cases where both vitreous humor and urine were analyzed showed consistent results, that is both specimens were positive or negative. This suggests that in the absence of additional information, a BAC of 0.04 g/dL or higher probably resulted from ethanol consumption.