Preliminary Screening Assays for Drugs of Abuse in Hair

Performing a preliminary screening test is a practical necessity for laboratories that process a large volume of hair samples. In workplace testing, a confirmation test is initiated only after a positive screening test. Although instrumental methods such as ion spray liquid chromatography (LC)-tandem mass spectrometry (MS-MS) (13) and gas chromatography (GC)-mass spectrometry (MS)-electron ionization (EI) (14,15) have been utilized to test for a number of analytes simultaneously, immunoassays such as radioimmunoassay (RIA) or enzyme immunoassay (EIA) are the modality most amenable to highvolume screening (16-21). The challenges of developing an immunoassay for hair samples involve solubilizing or extracting the samples, achieving the level of sensitivity required, managing possible matrix effects (nonspecific interference which, if unchecked, could cause both false-negatives and -positives), and minimizing cross-reactivities. All of these components will impact the sensitivity and specificity, precision, and accuracy of the test.

Analysis for the presence of the drug opiates in hair was performed using RIA as early as 1979 (22). This was followed soon after with tests for phen-cyclidine (PCP) (23) and cocaine (24). In fact, it was the availability of RIA as an ultrasensitive analytical tool that initially prompted the pioneering testing of drugs in hair. As enzyme immunoassays develop greater sensitivity, nonradio-active immunoassays are increasingly being used for hair testing. A review of the immunological methods for testing drugs in hair from the early period to the year 2000 has been presented by Spiehler (25). MS confirmation methods took a few additional years to achieve the necessary sensitivities.

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