Clinical performance of a new lateral flow immunoassay for xylazine detection

Objectives: Xylazine is a potent sedative used in veterinary medicine. Recently, recreational drugs such as fentanyl have been found to contain xylazine, increasing the risk of respiratory depression and death. Despite a similar presentation to opioid overdose, patients who ingest xylazine do not respond to treatment with Narcan. Therefore, rapid detection of xylazine could improve patient management and prevent adverse outcomes.

Methods: We evaluated the XYL500 one-step xylazine drug of abuse test for its ability to detect xylazine in 152 urine samples from patients on chronic opioid therapy for pain management or in treatment for substance use disorder. Results were compared to LC-MS/MS as the reference method. Precision, cross-reactivity, interference and stability studies were performed.

Results: Pooled patient samples were consistently negative or positive when tested five times on the same day and over three days of testing. The diagnostic sensitivity, specificity and accuracy of the XYL500 assay were 74, 98, and 82 % respectively, as compared with LC-MS/MS. XYL500 detected 77 of the 104 LC-MS/MS positive samples identified in our initial evaluation, including some that contained low levels of xylazine (n=8), <10 ng/mL. Minimal cross-reactivity with other opioid analgesics and commonly encountered drugs was seen with only one false positive result. Interferences by common urine contaminants were negligible. Specimens were stable up to 160 days refrigerated and up to 80 days at room temperature.

Conclusions: XYL500 allows for rapid detection of xylazine, illustrating its utility in monitoring patients who ingested recreational drugs containing the additive, xylazine, and its potential to improve patient management.