Question: For adults addicted to drugs and alcohol (sub groups include heroin, cocaine, crack, amphetamine and alcohol) how accurate is hair strand drug and alcohol testing, when compared to mouth swabs, urine testing and breathalysers in achieving accurate testing of drug and/or alcohol use?


Four small studies assessed hair strand testing drug and alcohol testing.   Only one study evaluated hair testing against a reference standard that classified participants according to their drug use status independent of the hair test results.  Data from the other studies can therefore not provide strong direct evidence on the accuracy of the hair test.   Generally there was support for hair testing for cocaine with the evidence suggesting that this is a highly sensitive and specific method and more accurate than urine or self report. Results were less clear for opiate use. One very small cohort study suggested that urine testing may be more appropriate for monitoring opiate use but this study was judged at high risk of bias. In contrast, the prevalence of a positive result was greater for the hair test than for the urine test in another study but lower than for self-report. It is likely that the timing of the test in relation to when the drug was used affects the accuracy of the test and so the choice of test is likely to be influenced by the setting in which the test will be used.  Methadone, cannabis, alcohol and amphetamine were each assessed in single studies and so it was difficult to draw conclusions.The limited data suggested that hair strand testing may have limited utility for cannabis testing.

The small number of studies in this area, and the lack of studies comparing hair testing against a valid reference standard mean that there is a need for further high quality studies assessing the accuracy of hair strand testing for drug and alcohol use.

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