Specimen collection and procedures
Decontamination procedures
Contaminants of hair would be a problem if they were drugs of abuse or their metabolites, or if they interfered with the analysis and interpretation of the test results. It is unlikely that anyone would intentionally or accidentally apply anything to their hair that contained a drug of abuse. The most crucial issue facing hair analysis is to avoid technical and evidentiary false positives. Technical false-positives are caused by errors in the collection, processing and analysis of specimens, while evidentiary false-positives are caused by passive exposure to the drug. Approaches to prevent evidentiary false positives through external contamination of the hair specimens have been described by Baumgartner and Hill (1992). Most, but not all, laboratories use a wash step; however, there is no consensus or uniformity in the washing procedures. Among the agents used in washing are detergents (such as shampoo), surgical scrubbing solutions, surfactants (such as 0.1% sodium dodecyl sulfate), phosphate buffer and organic solvents (such as acetone, diethyl ether, methanol, ethanol, dichloromethane, hexane or pentane) of various volumes for various contact times. Generally, a single washing step is used, although a second identical wash is sometimes performed. If external contamination is found by analysing the wash solution, the washout kinetics of repeated washing can demonstrate that contamination is removed rapidly. According to Baumgartner and Hill (1992), the concentration of drug in the hair after washing should exceed the concentration in the last wash by at least ten times. It has also been proposed that hair should be washed three times with phosphate prior to analysis, to remove any possible external contamination, and that the total concentration of any drug present in the three phosphate washes should be greater than 3.9 times the concentration in the final wash. Detection of drug metabolite(s) in hair that cannot be explained by hydrolysis or environ mental exposure unequivocally establishes that internal drug exposure has occurred (Cone et al. 1991). Cocaethylene and norcocaine would appear to meet these criteria, as these metabolites are only formed when cocaine is metabolised. As these metabolites are not found in illicit cocaine samples, they would not be present in hair as a result of environmental contamination, and thus their presence in hair could be considered a marker of cocaine exposure. This procedure can be extended to other drugs. However, there is still great controversy about the potential risk of external contamination, particularly for crack, cannabis and heroin when smoked, as several authors have demonstrated that it is not possible to remove these drugs fully using wash procedures (Blank and Kidwell 1995; Kidwell and Blank 1996). In conclusion, although it is highly recommended to include a decontamination step, there is no consensus as to which procedure performs best, so each laboratory must validate its own technique.
