Performance of Xylazine Test Strips

"This study examined the performance of BTNX XTS [Xylazine Test Strips] for testing drug residue. The detection of xylazine’s presence was lower than expected although increased if xylazine was the sample major psychoactive component. Our findings suggest further research and field testing are needed to develop rapid XTS and procedures for residue testing in point-of-care DCS.

"Few studies have evaluated the performance of XTS in the community. One small laboratory study on samples from Philadelphia found no false-negatives compared to confirmatory results (i.e., a sensitivity of 100 %). Notably, the Philadelphia study tested samples rather than residue using a 1 mg:1 mL dilution factor (Krotulski et al., 2023), compared to our procedure of dissolving an unquantified amount of residue in 5 mL of water. A second study using 100 residue samples from Maryland and Nevada assessed crossreactivity of 77 different compounds found only lidocaine produced false-positives (Sisco et al., 2023). Each study tested different XTS batch lots which may have contributed to result discrepancies; quality and accuracy of lateral flow strips can vary between lots (Hayden et al., 2014).

"This study's limitations include its small sample size, limited collection radius and timeframe, and non-random collection procedure. Tested samples primarily contained fentanyl or other opioids; further research should explore the performance of testing non-opioids. Additionally, no validated procedure existed for testing drug residue at the time of the study. While collecting larger amounts of drugs to test would likely increase generalizability and confidence in findings, non-laboratory DCS fall into a legal gray area due to the Controlled Substances Act and resultantly often rely on drug refuse residue. Finally, while quantification was outside the scope of this study, it would provide stronger evidence of whether XTS perform in accordance with their stated detection limit in a community setting and should be considered for future studies. Given these uncertainties, our findings, while initial, caution against reliance upon the XTS alone for xylazine detection in drug residue and, if used, should be accompanied by a thorough discussion of the test’s limitations when interpreting the results or coupled with laboratory testing."