Comparative alcohol concentrations in blood and vitreous fluid with illustrative case studies

The Toxicology Bureau of the New Mexico Department of Health performs drug and alcohol testing on approximately 2800 medical examiner cases each year across the entire state. Although blood is usually the preferred specimen for alcohol analysis, the importance of multiple specimen analysis in alcohol-related death investigation is well understood. Quantitative alcohol determination in a variety of postmortem specimens may provide important interpretive information. In a total of 322 consecutive cases, blood and vitreous alcohol concentrations were compared. No alcohol was detected in either specimen in only 27 of the cases. In the remaining 295 investigations, alcohol was detected in the vitreous fluid, blood, or both. Analysis of the data and presentation of case studies reinforce the need for multiple specimen analysis in alcohol-related death investigation. Postmortem blood and vitreous alcohol concentrations were compared in a series of 295 alcohol-positive cases. The vitreous alcohol concentration (VAC) exceeded the blood alcohol concentration (BAC) in 209 cases (71%). Blood alcohol concentrations exceeded vitreous concentrations in 81 cases (27%), and the concentrations were equivalent in 5 cases (2%). For the purpose of this study, samples that were negative in both specimens were excluded. In casework where the VAC > BAC, linear regression analysis indicated an R2 value of 0.958 (n = 209) and a VAC approximately 16% higher than the BAC. The VAC/BAC ratio was more variable at lower BACs (< 0.1 g/100 mL). The source of blood for this data set was predominantly femoral (n = 203), followed by heart (n = 5) and pleural cavity (n = 1). Although VAC/BAC ratios were more consistent at concentrations of 0.1 g/100 mL and above, the overall ratio ranged from 1.01 to 2.20. Of the 81 cases where BAC > VAC, a total of 24 cases indicated no vitreous alcohol. The range of blood alcohol concentrations among these cases was widely variable (0.01 to 0.30 g/100 mL). Unlike the VAC/BAC data set which consisted of 97% femoral blood, the source of blood in the BAC > VAC data set was slightly more variable. Of the 81 cases where BAC > VAC the blood source consisted of femoral (n = 68), heart (n = 8), pleural cavity (n = 2), carotid (n = 1), jugular (n = 1), and chest blood (n = 1). All analyses were conducted using dual-column gas chromatography with flame-ionization detection (GC-FID) with a reporting limit of 0.01 g/100 mL ethanol in postmortem samples. A series of case studies are used to demonstrate postmortem interpretive issues and the benefits associated with multiple specimen analysis. Cases include postmortem production of ethanol, rapid or unexpected death during the absorptive phase, and site-dependent differences following traumatic injury. Actual case studies involving other volatile organic compounds are also presented including isopropanol and acetone from endogenous and exogenous sources. Many of these cases studies highlight the difficulty associated with postmortem alcohol interpretation in the absence of multiple specimens or adequate case history.