What constitutes a positive result in hair analysis: proposal for the establishment of cut-off values

Hair is still a seldom used specimen in most laboratories but its analysis has the potential of making a valuable contribution. Despite the many worthwhile reports, the scientific community at large still has reservations about the validity of hair analysis. Some of this is due to a lack of consensus among the active investigators on how to interpret the results from an analysis of hair. In USA, passive exposure seems to be a major problem, which can only be eliminated with difficulty. On the other hand, in Europe, scientists are performing standard decontamination procedures. It would be very helpful if a group of active researchers on hair analysis, representative of academic, government and private laboratories could define what are the areas of agreement and what are the issues that require further efforts to get a consensus. We propose the following guidelines: (1) a complete decontamination procedure, including the analysis of the wash solution; (2) two distinct analytical methods (immunoassay and GC/MS, or two different GC/MS methods); (3) the establishment of cut-off values (using 30-mg hair samples), 0.5 ng/mg of 6-MAM in the case of heroin abuse, and 1 ng/mg of cocaine in the case of cocaine abuse, which can be decreased to 0.5 ng/mg when use is supported by other evidence of drug intake.