Comparison of assay methods for benzodiazepines in urine. A receptor assay, two immunoassays, and gas chromatography-mass spectrometry.

We analyzed 127 urine samples for benzodiazepines by a radioreceptor assay and two immunoassays (cloned enzyme donor immunoassay [CEDIA, Boehringer Mannheim, Indianapolis, Ind] and agglutination immunoassay [ONLINE, Roche Diagnostic Systems, Branchburg, NJ]). Sixty samples that were positive by at least one of these assays were submitted to gas chromatography-mass spectrometry, which detected benzodiazepines such as oxazepam, nordiazepam, and lorazepam in 44 samples. Diagnostic sensitivity and specificity of the receptor assay were almost equal or superior to those of the two immunoassays, although discrepant results were obtained in some samples. The discrepancies resulted from differences in the cross-reactivity of these assays. For example, the receptor assay could detect lorazepam, while the two immunoassays could not, and CEDIA was interfered with by a metabolite of sertraline while the others were not. This is the first report showing the utility of a receptor assay for screening benzodiazepines in urine.