False interpretation after a hair test can be observed in case of laboratory mistakes, external contamination from environmental pollution or after drug incorporation into the hairy element from body fluids after corpse decomposition. The last situation is known as postmortem artefact. Despite 35 years of research, it appears that postmortem artefact cannot be excluded in some forensic cases, despite the use of sophisticated decontamination procedures. Therefore, the careful interpretation of the results is a daily challenge. By the past, it has been proposed that segmental hair analysis would help in adequate interpretation. However, in a recent series of cases involving decomposed bodies, it was not possible to do segmental analysis, because the hair was too short (<3cm). In these 6 cases, the pathologist was able to collect during the autopsy, hair and putrefied remains. Several drugs were identified and quantified in hair after hot water and dichloromethane decontamination. In all cases, the measured concentrations were 2 to 400 times higher than the highest published concentrations. Most of these drugs were also identified in putrefied human material, indicating ante mortem exposure. These unusual hair concentrations were considered as the sign of external contamination by decomposed fluids and that it is not possible to document long-term exposure before death with the results. It is concluded that testing for drugs in hair collected from a decomposed body can document ante mortem drug exposure within the last hours before death, but should not be used to demonstrate repetitive drug use. This new series of results strongly supports our earlier findings about the risk of misinterpretation of hair results.Le texte complet de cet article est disponible en PDF.
Keywords : Hair, Postmortem, Putrefaction, Contamination, Drug, Interpretation