Evaluating the Sensitivity, Selectivity, and Cross-Reactivity of Lateral Flow Immunoassay Xylazine Test Strips

The rise of xylazine-adulterated substances poses significant public health risks due to their severe side effects, creating an urgent need for reliable detection methods. Lateral flow immunoassay-based xylazine test strips (XTS) have emerged as a potential harm reduction tool for quick, easy, and field-based drug checking, but their effectiveness remains underexplored. Although commercial XTS from multiple vendors are available, the lack of regulatory standards raises concerns regarding their accuracy.

This study evaluated the performance of commercially available XTS from 7 different vendors to investigate the interproduct comparison of sensitivity, precision, cross-reactivity, and stability over changes in human urine pH and extended storage under ambient and extreme temperature conditions.

All test strips maintained their sensitivity, reproducibility, and effectiveness despite urinary pH fluctuation and storage temperatures over 6 weeks. However, concentration-dependent false-positive results were observed when the strips were tested with drugs and adulterants commonly encountered in seized samples. Interfering compounds including lidocaine, levamisole, ketamine, methamphetamine, diphenhydramine, promethazine, and cetirizine displayed varying degrees of cross-reactivity with different XTS.

This study underscores the variability in performance among commercially available XTS, highlighting their implications for use in harm reduction and forensic settings. While XTS are capable of detecting xylazine at low concentrations, the potential for false-positive results due to cross-reactivity with other drugs necessitates caution in their interpretation. Hence, XTS may serve as a viable harm reduction tool, provided that their cross-reactivity limitations are thoroughly documented and they are incorporated as part of a broader harm reduction strategy.