The two-stage drug-testing strategy requires the use of analytical methodologies with different chemical principles. Analytical methodologies for drug testing can be grouped into three major categories. Each of these technology categories can be further broken down into multiple selections for instrumentations and methods. Bio-affinity-based binding assays such as immunoassays are commonly used for screening. Separation techniques such as chromatography or electrophoresis, as well as their coupling with powerful detectors such as mass spectrometers, can be effectively used for confirmatory testing of preliminary positive results or systematic analysis of generally unknown toxic compounds. The analytical technologies afford a powerful means toward the detection, identification, and quantification of the presence of abused drugs in biological specimens. Nevertheless, measurement uncertainties and experimental variations always exist. Therefore, the interpretation of analytical results requires the understanding of the performance characteristics and limitations of the techniques used for analysis. In addition, the overall interpretation of drug-testing results has to be considered in the context of both the reasons and the scenarios for testing (209-212). Substance abuse can play various roles in different cultural and occupational settings; hence it is important to understand the nature of drugs-of-abuse testing and how to correlate results from one situation to another.

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