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

Background The rise of xylazine-adulterated substances poses significant public health risks due to its severe side effects and this pressing concern calls for reliable xylazine 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 absence of regulatory standards raises concerns regarding their accuracy and effectiveness. Method This study evaluated the performance of commonly used commercially available XTS from different vendors to investigate the inter-product comparison of sensitivity, precision (reproducibility and robustness), cross-reactivity, and stability over changes in pH and extended storage under ambient and extreme temperature conditions. Results All test strips demonstrated effective sensitivity, and reproducibility and maintained their efficacy despite changes in urinary pH and storage temperatures over six weeks. Interfering compounds including lidocaine, levamisole, ketamine, methamphetamine, diphenhydramine, promethazine, and cetirizine displayed varying degrees of cross-reactivity with different XTS. Conclusion This study highlights the variability in performance among commercially available XTS, with implications for their use in harm reduction and forensic settings. While XTS can detect xylazine in low concentrations, the potential for false positives due to cross-reactivity with other drugs necessitates caution in their interpretation. Hence, xylazine test strips 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.