Forensic Drug Testing For Opiates. IV. Analytical Sensitivity, Specificity, and Accuracy of Commercial Urine Opiate Immunoassays

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Abstract
Four commercial immunoassays, TDx® Opiates (TDx), Coat-A-Count® Morphine in Urine (CAC), Abuscreen® Radioimmunoassay for Morphine (ABUS) and Emit® d.a.u.™ Opiate Assay (EMIT), were tested for sensitivity, specificity, and accuracy with urine specimens containing known amounts of opiates and opiate metabolites. The immunoassays were evaluated in a semiquantitative mode by comparison of morphine equivalents to GC/MS assay of free and total morphine and codeine or to target concentrations. In all cases, the apparent sensitivities of the assays were higher than those required for detection of morphine at cutoffs mandated by the Health and Human Services guidelines for testing of Federal workers. The apparent specificities of the immunoassays varied considerably. The CAC assay was found to be highly selective for free morphine, whereas TDx, ABUS, and EMIT demonstrated broad cross-reactivity with other opiates. Comparison of semiquantitative results from the immunoassays with GC/MS data indicated a high degree of accuracy for determination of morphine levels. Generally, the patterns of sensitivity and cross-reactivity were unique for each assay, indicating that a detailed knowledge of assay performance characteristics is necessary for accurate interpretation of forensic urine testing data.

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