Analytical performance and visual evaluation of test strips for fentanyl.

Abstract Background Testing street drugs for the presence of active drugs and drugs used as adulterants such as fentanyl can provide the user some confidence as to the safety of their pills. As such, disposable testing strips have become available through multiple vendors as a tool set to combat adulterants. Because there is not currently an industry standard for these products, they can vary in specifications and quality. This study serves as a broad evaluation survey across multiple vendors to compare performance and assess the best product for harm reduction. Methods We obtained 6 different commercially available different commercially available fentanyl test strips and evaluated them for analytical sensitivity using drug standards. The specificity of the fentanyl strips against fentanyl analogues was also assessed. Powdered fentanyl standards and analogues were initally dissolved in methanol and then serially diluted in water to bracket the manufacturer’s stated test strip sensitivity. Each dilution was tested in duplicate until a negative result was obtained. The ability to discern positive from negative results under different lighting conditions by two observers in duplicate, was also assessed for these strips including different lots for some. Results Three of the fentanyl strips had the best sensitivity (at 3.6 ng/mL each), well below the stated sensitivity of 10, 20, and 200 ng/mL. The other three were less sensitive (at 7.2, 29 ng/mL). For specificity against fentanyl analogues, all of the strips tested positive for all of the analogues tested, but at different levels. The visual endpoints for all of the strips were acceptable under normal lighting conditions, but cannot be read when the ambient light is low. The readability at different dwell times are noted. Conclusion Based on these results, we determined that the WPHM and Hangzhou SingClean fentanyl test strips had the best analytical sensitivity (3.6 ng/mL). The Henso strip had lower sensitivity but the best discrimination between positive and negative signals. Each of the fentanyl strips had varying degrees of specificity and visibility towards fentanyl drug analogues.