Evaluation of a Benzodiazepine Immunoassay for Urine Drug Testing in Clinical Specimens

Benzodiazepines are commonly prescribed medications frequently linked to instances of abuse and overdose. Historically, FDA-cleared benzodiazepine urine immunoassays cross-react poorly with glucuronidated benzodiazepine metabolites, leading to false negatives. Clinical laboratories have addressed this deficiency by creating laboratory-developed tests (LDTs) that incorporate a beta-glucuronidase hydrolysis step to increase the clinical sensitivity of these assays.

Performance characteristics of 2 FDA-cleared benzodiazepine urine immunoassays (Benzodiazepines Plus, no glucuronidase and Benzodiazepines II, with glucuronidase; Roche Diagnostics) and a previously described benzodiazepine immunoassay LDT (with glucuronidase) were evaluated using 258 clinical urine specimens. The positive immunoassay cutoff was set at 200 ng/mL of nordiazepam and results were compared to an LC-MS/MS benzodiazepine LDT. Clinical sensitivity, specificity, precision, and immunoassay cross-reactivity were determined for all 3 immunoassays.

The Benzodiazepines II and LDT immunoassays exhibited greater clinical sensitivity (100% and 95.2%) compared to the Benzodiazepines Plus assay (66.7%). Clinical specificity of 100% was observed for all 3 assays. Immunoassay response of the Benzodiazepines II assay was greater across the range of concentrations tested (100-1000 ng/mL) relative to the other immunoassays and was the most sensitive immunoassay for the detection of lorazepam glucuronide.

The Benzodiazepines II immunoassay demonstrated the greatest clinical and analytical sensitivity compared to the Benzodiazepines Plus and LDT immunoassays. The incorporation of beta-glucuronidase was crucial, as the Benzodiazepines II and LDT immunoassays demonstrated superior clinical sensitivity when compared to the Benzodiazepines Plus immunoassay that does not incorporate a beta-glucuronidase hydrolysis step.