The emerging new psychoactive substances made available for recreational drug use have recently started to include designer benzodiazepines. As a consequence, the routine immunoassay drug testing for benzodiazepines may become less effective, due to an increased occurrence of ‘false negative’ and ‘false positive’ results. This work aimed to extend the knowledge of analytical cross‐reactivity of 13 designer benzodiazepines in the CEDIA, EMIT II Plus, HEIA, and KIMS II immunoassays. Urine standards were prepared by spiking blank urine with clonazolam, deschloroetizolam, diclazepam, estazolam, etizolam, flubromazepam, flubromazolam, flutazolam, 3‐hydroxyphenazepam, meclonazepam, nifoxipam, phenazepam, and pyrazolam. Authentic urine samples from intoxication cases identified by liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) were also investigated. For the spiked standard samples, the 13 designer benzodiazepines generally showed a high cross‐reactivity in all assays. This was further confirmed when investigating their detectability in authentic urine samples from cases of drug intake. The test responses also indicated additional reactivity from metabolites. The lowest detectability in spiked samples was observed for flutazolam, which shows the most divergent chemical structure compared with the other benzodiazepines. Overall, the KIMS II and CEDIA immunoassays, which both include enzymatic hydrolysis of conjugated forms, showed the highest, and EMIT II Plus the lowest degree of reactivity, for spiked parent substances and authentic urine specimens. The results of this study demonstrated that designer benzodiazepines can be detected in standard urine immunoassay drug screening and this should be taken into consideration when performing confirmation analysis. Copyright © 2016 John Wiley & Sons, Ltd.
