Performance of Xylazine Qualitative Immunoassays Designed for Drug Checking in Urine Samples

Xylazine is a public health threat for individuals who use drugs. Data informing xylazine concentrations are hampered by a lack of point-of-care urinalysis testing. This study evaluated the performance of qualitative immunoassay strips designed for drug checking in identifying xylazine in urine samples.

The ability of 2 noncleared xylazine qualitative immunoassay test strips (W.H.P.M. Inc, 500 ng/mL and Rapid Response [BTNX Inc., 1000 ng/mL]), developed for use in drug-checking paradigms, to detect xylazine in urine samples of persons presenting for opioid use disorder treatment was evaluated. Samples were tested using each test strip twice, and consensus results were compared with results from quantitative LC-MS/MS analyses (5 ng/mL).

Quantitative testing revealed 67% (71/106) samples tested positive for xylazine >5 ng/mL. Concentrations ranged between 5.3 and 30,900.50 ng/mL, 12 of which exceeded >500 ng/mL and 6 of which exceeded >1000 ng/mL. W.H.P.M. Inc. showed excellent sensitivity and specificity (92% and 94%, respectively) at the 500 ng/mL threshold but did not detect 63% of true positive samples (ie, those that tested positive in the quantitative testing >5 ng/mL). Rapid Response also had excellent sensitivity and specificity (100%, 100%, respectively) at the 1000 ng/mL threshold, but did not detect 74% of true positive samples.

Two immunoassay strips designed for drug checking showed strong sensitivity and specificity at their detection thresholds; however, most samples testing positive for xylazine were below those thresholds, resulting in most participants with true xylazine exposure not being accurately identified. Prospectively designed urine point-of-care strips are necessary to help inform the relationship between xylazine exposure and its related consequences.