Cocaine and metabolites may be detectable in hair for longer periods of time than urine. For this reason, analysis of hair is useful in determining a past history of cocaine use. It takes 4–5 days for ingested cocaine to begin to appear in the hair. The ability to detect cocaine in hair is based more on concentration than a pharmacological “time window” since as long as the hair is not cut, incorporated drug will remain in it.
Many important issues related to hair testing are still being studied including environmental contamination, washing techniques, racial bias in hair based on the concentration of certain types of
melanin, sex bias, specimen adulteration, quality control procedures, proficiency testing and the establishment of cutoff concentrations.
In order to minimize environmental contamination issues and to demonstrate cocaine ingestion, the proposed guidelines for hair testing in federal workplace drug testing programs require a benzoylecgonine/cocaine ratio of > 0.1 in the confirmatory testing process in order to report a positive result
Read more information on these links:http://www.druglibrary.org/Schaffer/cocaine/cokehair.htmhttp://mass-spec.chem.cmu.edu/VMSL/cocaine/ch_bg5.htm
The incorporation of cocaine and metabolites into hair: effects of dose and hair pigmentationhttp://dmd.aspetjournals.org/cgi/reprint/28/12/1464.pdf#search=%22Cocaine%20%2BHair%22
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