Determination of drugs of abuse in hair: evaluation of external heroin contamination and risk of false positives.

One of the most controversial point regarding the validity of hair testing is the risk of false positive due to external contamination. The aim of our experience is to verify if a 5 consecutive days contamination with a small amount of a powdered mixture of heroin hydrochloride and acetylcodeine hydrochloride (10:1 w/w) will last sufficiently long to make a contaminated subject indistinguishable from active users, and if normal washing practices together with the decontamination procedure are sufficient to completely remove the external contamination. Our results suggest that decontamination procedures are not sufficient to remove drugs penetrated into hair from external source. In fact, all contaminated subjects were positive for opiates (heroin, 6-MAM, morphine, acetylcodeine and codeine) for at least 3 months. Significant 6-MAM concentrations (>0.5 ng/mg) were found in each subject until 6th week. Further, 6-MAM/morphine ratio were always above 1.3.