Does external exposure to certain drugs like marijuana or crack smoke affect the Hair Test results?

All hair samples that produce a positive screening result are washed extensively to remove external contamination and may be re-screened for the potential positive drug. If the secondary hair screen is positive and the ratio of the wash solution is greater than 10% of the confirmation result, the sample is contaminated. If the ratio of the wash solution is less than 10% of the confirmation result, the sample is positive. Marijuana does not follow the wash patterns of the other drugs. To rule out the possibility of external contamination for marijuana, detection of only metabolite (THC-COOH), which is only produced by the body and cannot be an environmental contaminant, is done.



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