Potential problems with the interpretation of hair analysis results

Due to differences in hair growth rare depending on anatomical region, age, gender, ethnicity and interindividual variability, interpretation of paren t drug or/and metabolite concentrations in hair is not easy. Furthermore, a s drug incorporation mechanisms into hair matrix is not yet fully understoo d, it is rather difficult to extrapolate details on time and dose from hair segment analysis. If incorporation sources other than from bloodstream (sk in secretions and/or external/environmental contamination) are considered, interpretation becomes even more complicated. For evaluating possible passi ve contamination, it is essential to consider specific identification of me tabolites, use of metabolite-to-parent drug ratios, assays of decontaminati on washes and analysis of specimens collected from other body parts. Cosmet ic hair treatment, natural and artificial hair colour, differences in hair structure and specificity of analytical methodology may represent other bia s sources affecting concentrations of drugs in hair. A suitable cut-off lev el related to the LOD will allow correct identification of drugs or metabol ites in hair. Regarding the performance of different hair testing laborator ies, little information is available at this time to what extent test resul ts are comparable and their interpretation is consistent. Frequency of drug consumption and time intervals between multiple consumption or lag time be tween consumption and appearance in the hair has not been fully investigate d and needs further research. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.