Introduction: There are previous publications showing the use of ethyl glucuronide (EtG), a non-oxidative metabolite of ethanol, as a marker of ante-mortem ingestion of alcohol in forensic autopsy cases. The problem of possible degradation or formation of EtG during putrefaction is however not well studied and the aim of this study was to investigate the possibility of false negative and false positive EtG results by an in vitro study. Further, we used the information from the in vitro study on real cases, to get an impression of the practical problem of degradation or formation of EtG.
Methods: An in vitro study was carried out to study the concentrations of EtG in blood samples under controlled conditions during putrefaction. In addition, to illustrate the practical problem of degradation or formation of EtG, we used routine samples analysed for EtG in blood. Blood samples from forensic autopsies with ethanol detected but EtG not detected in blood, and therefore suspected post-mortem ethanol formation, were identified. Fifteen such cases had urine samples available, and these were analysed for EtG. We hypothesised that since concentrations are often higher in urine, there would still be traces of EtG left in this medium if post-mortem degradation was the reason for the negative result in blood.
Results: In this in vitro experiment, EtG was very unstable in blood samples at 30/40 degrees C without preservatives. On the other hand, EtG was stable with potassium fluoride at room temperature, and there was no formation of EtG either at 30 degrees C without preservatives, or at room temperature with potassium fluoride. Of the 15 routine cases where EtG in blood was negative, and the ethanol detected was assumed endogenous, six were positive for EtG in urine. In these cases, ethanol was probably ingested, and the negative EtG in blood may be a false negative result due to degradation during putrefaction.
Conclusion: Analysis of EtG in blood is a helpful tool to determine in vivo ingestion of ethanol in post-mortem cases. A negative result, however, especially in heavily putrefied cases, must be interpreted with caution. Analysis of an additional medium would be valuable in these cases.