Xylazine has emerged as a major adulterant in the unregulated drug supply in recent years. Initially common in certain cities such as Philadelphia, it is now found in communities across the United States. The veterinary sedative can prolong the effects of fentanyl, but has been linked to various harms, including deep skin ulcers and injection wounds that won’t heal.
Many people who use drugs want to avoid xylazine. So several companies have seized the opportunity to develop xylazine test strips (XTS) which, mirroring fentanyl test strips, are designed to quickly and easily determine whether xylazine is present in a substance.
XTS are unregulated and were developed very quickly, leading many to question whether they can be trusted. A new study, published in the Journal of Applied Laboratory Medicine, offers the first broad evaluation of seven commercial XTS products.
Reassuringly, all test strips reliably detected the presence of xylazine, even at very small doses and under extreme conditions. However, they also frequently produced false positives when exposed to a range of common drugs.
While the packaging of each XTS brand lists its sensitivity—the minimum xylazine dosage required to trigger a positive result—these performance claims are not always reviewed by third-party testers. The new study, whose authors report no financial ties to any XTS manufacturer, provides a much-needed quality check.
“We focused on evaluating if and how much they are different in performance from each other and if they are meeting the performance criteria or not,” coauthor Dr. Saman Majeed, of the University of North Carolina Asheville, told Filter.
These results demonstrate the trade-offs associated with selecting a brand of XTS. Some strips detected xylazine at incredibly small doses, but were also highly susceptible to producing false positives.
The research team tested strips from seven vendors under a range of conditions, including extended storage at extreme temperatures. The vendors were 12 Panel Now, BTNX, DanceSafe (manufacturer WHPM), MD-Bio, Medimpex, WaiveDx and WiseBatch.
“The good thing is that they all give positive results for xylazine even after exposing [them] to all different conditions,” Majeed said. While all brands detected xylazine at low concentrations, 12 Panel Now was particularly sensitive.
However, the study uncovered a significant challenge: cross-reactivity. When exposed to substances such as lidocaine, methamphetamine, ketamine and Benadryl, many of the strips produced false positives. The degree of cross-reactivity varied widely among test-strip brands. The BTNX strips produced a false positive only for methamphetamine, while newer brands 12 PanelNow and Medimpex displayed cross-reactivity with almost every substance tested.
These results demonstrate the trade-offs associated with selecting a brand of XTS. For example, the 12 PanelNow strips detected xylazine at incredibly small doses, but were also highly susceptible to producing false positives.
Table by Sydney Sauer, based on the study findings. “False positive” means that a false positive was produced at least once, out of several tests—but not necessarily every time.
When choosing between brands, consumers should look for strips that come with clear use instructions and have been rigorously tested and reviewed by independent researchers.
“There are many products out there that have not been independently, scientifically tested,” study coauthor Dr. Ju Nyeong Park, of Brown University, told Filter. “If I had to pick a brand, I would probably pick a brand that has been vetted at least once, if not multiple times, by different research groups.”
Currently, there is no centralized resource for checking which brands have been externally vetted, however.
“I would love to see the CDC or SAMHSA, or even the NIH, dedicate a website to this topic because clearly there’s a lot of need,” Park said. For now, she recommends contacting drug checking organizations like Street Check and Remedy Alliance for technical assistance.
“For me, the takeaway is that we still do need … more comprehensive models of drug checking programs.”
In addition to warning of the potential for false positives, the authors cautioned against taking negative results as evidence that a certain substance is safe for consumption. Just like fentanyl test strips, XTS lines can be faint and difficult to discern—especially in low-light environments like nightlife venues. And even when the result is clearly negative, the sample could still contain other substances that the person doesn’t want to ingest.
Due to these limitations, Park stressed the importance of continuing to develop full-scale drug checking services for community use.
“For me, the takeaway is that we still do need … more comprehensive models of drug checking programs,” she said. “I think that’s really important to highlight because any sort of test that you use in the community is more likely … to be less accurate than a lab.”
As a simple, portable option with relatively easy-to-interpret results, XTS are still a powerful harm reduction tool, considering their high detection rates in the lab. As more test strips and other portable testing options emerge, continued review by third-party experts will be essential.
“We really need a lot of performance evaluation studies, not only for xylazine test strips, but for all the drug testing strips in the market,” Majeed concluded.
Top photograph by Defense Visual Information Distribution Service via itoldya – GetArchive/Public Domain
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