Performance of a Xylazine Test Strip in Urine Biospecimens.

OBJECTIVE

Herein, we evaluate the performance of xylazine test strips (XTS) in urine samples. XTS is used for community drug checking (powders and liquids) but lacks regulatory approval for human specimen testing.

METHODS

We obtained n=85 human urine specimens from a toxicology laboratory in Philadelphia, originally submitted for qualitative mass spectrometry (MS) expanded drug analysis. Residual urine was tested for xylazine using XTS (BTNX Inc.), and results were then compared against the MS method. Synthetic urine spiked with xylazine standards was used to determine the XTS cutoff. An external quantitative MS method was used to investigate potential mismatches.

RESULTS

Of n = 85 human urine specimens, XTS demonstrated 86% sensitivity and 93% specificity using a XTS cutoff of 750 ng/mL established with synthetic urine samples. Six false negatives (14%) among 43 qualitative MS-positive samples were observed, primarily due to XTS's lower sensitivity. Among 3 false positives (7%) observed in 42 qualitative MS-negative samples, lidocaine likely causes the interference. Interestingly, some XTS-positive samples were found to have xylazine concentration lower than 750 ng/mL using quantitative MS, suggesting cross-reactivity with unknown metabolites or analogs.

CONCLUSIONS

XTS requires further refinement to achieve lab-quality performance, with a focus on improving sensitivity and minimizing false positives caused by nonspecific interactions with urine components. Further research is necessary to optimize their design, establish accurate detection thresholds, supporting clinical decision-making, and obtain regulatory validation.