Rapid Immunoassay Detection of Xylazine in Urine Samples in Emergency Department Patients With Opioid-Related Toxicity

Xylazine, a veterinary sedative and adulterant in the illicit fentanyl supply, is frequently unrecognized in patients presenting with opioid-related toxicity. No point-of-care test exists for xylazine, and many blood tests do not provide real-time results. Immunoassay test strips are a common harm reduction tool for patients to test an individual drug supply for fentanyl and adulterants. We evaluated rapid drug-checking test strips for xylazine detection in patient urine specimens and compared urine results with measured blood xylazine concentrations.

We conducted a prospective, single-site observational study of ED patients with suspected opioid overdose in New York City (April–July 2025). Waste urine and blood samples were analyzed when available. Urine testing was performed using two qualitative xylazine immunoassays: Instanosis (1 ng/mL detection threshold) and BTNX (1000 ng/mL). Blood xylazine concentrations were measured using Liquid Chromatography–Quadrupole Time-of-Flight Mass Spectrometry (LC-QTOF-MS).

Twenty-three urine samples and twenty-two corresponding blood samples were analyzed; one urine sample was missing a corresponding blood sample. Xylazine was detected in 16 blood samples (72.7%), with concentrations ranging from <0.1 ng/mL to 8.2 ng/mL. Instanosis detected xylazine in sixteen urine samples (69.6%), while BTNX detected xylazine in three samples (13.0%). Seven urine samples tested negative on both assays, and these samples had corresponding blood concentrations below detection thresholds. Twelve urine samples were positive on Instanosis but negative on BTNX. These 12 samples had corresponding blood samples with xylazine detected. No false-positive urine test strip results were observed.

Rapid xylazine immunoassays detected xylazine in urine samples for ED patients with opioid-related toxicity, with results confirmed by LC-QTOF-MS. Lower detection threshold assays demonstrated greater sensitivity. Drug-checking test strips may represent a feasible point-of-care tool to support clinical recognition of xylazine exposure in ED settings.