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Abstract
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From: 30th meeting of SFTA- 59th meeting of TIAFT - September 2022
Aim
Alcohol is the most determined substance in postmortem toxicology and its interpretation is especially complicated. Although the determination and quantification of ethanol is preferably carried out on blood samples, the determination of this parameter in other biological matrices can prove to be quite important. This may be true, for example, in cases where the blood sample available is insufficient or is in a state deemed unsuitable (e.g. putrefaction or contamination by other biological fluids such as gastric contents). Among the biological samples which can be considered as an alternative to blood in the determination of ethanol, the vitreous humor (VH) appears as the most interesting. Therefore, it is of high relevance the analysis of other biological samples, as urine and VH, that in normal situations are only positive for alcohol when antemortem ingestion has occurred. This is important mostly when the blood alcohol concentration (BAC) is lower than 0.5g/L. Another study reported that with a BAC of 0.5g/L there is an 87% probability of a positive result for alcohol in VH and with the increase of this concentration the probability goes up to 99%. In the present study, the authors made a statistical survey, within the period of three years, of the cases that indicated putrefaction in which the medical expert required the analyses of the BAC. From all the cases evaluated, three forensic cases were selected, which represent situations that might occur when studying the BAC of a putrefied corpse. These cases were chosen to highlight the possible benefits of analyzing multiple biological samples, when present, for confirmation of the BAC.
Method
The samples analysis was made using an Agilent 6890N gas chromatograph equipped with a flame ionization detector and coupled to an Agilent G1888 headspace injector of fixed volume (1mL) (HS-GC/FID). Prior to gas-chromatography analysis, all specimens, including the calibrators, were diluted 1:10. With this purpose, 100μL vitreous humor, urine and blood were diluted with 1mL aqueous solution of n-propanol (100mg/L), used as internal standard.
Results
In the period of 3 years (2018-2020), there were 4264 medical-legal autopsies executed in which the medical expert required the determination of the BAC. Of these cases, a total of 130 had information stating the presence of putrefaction. They were related to different causes of death (intoxication, drowning, trauma, natural deaths and undetermined cause) and had a postmortem interval between one and six days. BAC measured determined 64 cases with a negative result and 66 with a positive result. Of these, 66.7% had a BAC between 0.1g/L and 0.5g/L, relevant as endogenous production might have happened, making the interpretation of these values challenging. However, this interpretation can benefit from the integration of the available case information, especially the search for alcohol in other biological samples. Using this data, it was determined how many cases presented one, two and three biological samples and three forensic cases were selected, representing each of these categories, exemplifying situations that can easily occur when studying the BAC of putrefied corpses.
Conclusion
In this study we discussed how the determination of the alcohol concentration in urine and VH can be a valuable tool, especially in the presence of putrefied corpses and low concentrations of alcohol in the blood, when trying to determine whether the BAC was of exogenous origin, endogenous production or both. This suggests that the analysis of these three types of biological samples (blood, urine, VH) can be of use in reaching a conclusion regarding the origin of the alcohol and making it less susceptible to dispute.
Language: en |