W6: Novelties in hair analysis and interpretation issues

Abstract

The importance of hair analysis is progressively increasing all over the world. In forensic toxicology, hair analysis is applied to various case types. In many countries, hair analysis plays an important role in the assessment of someone‘s driving ability or the proof of a maintained abstinence. Hair analysis can help to determine a previous exposure to a substance in postmortem investigations. Furthermore, hair analysis was successfully applied to the investigation of drug facilitated sexual assault claims, as well as child custody investigations. The detection of drugs in the hair is generally considered as a proof of ingestion or exposure to the drug in the recent past. In recent years, more and more cases have been described where segmental analysis of hair revealed the presence of a substance in multiple segments while the case circumstances however did not indicate a previous exposure. It seems likely that agonal processes caused an external contamination of the hair shaft through sebum or sweat. In drug/alcohol abstinence control, the consumption behavior of the last months can be monitored; the examined time window is defined by the length of the hair strand. It is well accepted that the hair samples should be collected in the vertex or occipital scalp region due to the most regular growth rates, this collection is however not mandatory. Recent studies have shown significant differences in concentrations when samples were collected from different regions of the scalp. Interpretation of hair analysis results is therefore becoming less straight forward and will require a more cautious approach. In summary, interpretation of hair analysis results requires even more the consideration of the latest developments and trends. The expert opinions should critically assess the validity of previously published data given the novel results.