B-342 Fentanyl Urine Drug Screen Comparison of the ARK II and Lin Zhi Immunoassays

Abstract Background Given the opioid epidemic, screening for fentanyl in urine has become increasingly important. Routine opiate immunoassays cannot identify fentanyl, given its structural variance from the more common opiates such as morphine and codeine. Therefore, the detection of fentanyl by immunoassay urine drug screen depends on antibody specificity for fentanyl. The ARK II is a widely used immunoassay that will detect fentanyl and norfentanyl. Recently, a novel fentanyl assay by Lin-Zhi has become available on the Roche platform; here, we evaluate its performance. Methods One hundred twenty nine urine samples were analyzed for fentanyl across the Lin-Zhi and ARK II assay on the Cobas c502 platform. Samples were either analyzed immediately upon request for drug of abuse screening or frozen for subsequent analysis. Liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) and/or prescription was used as confirmation for the presence of fentanyl. Our of the total 129 tested samples, so far 59 have been confirmed and additional studies are ongoing. The mass spectrometry assay has a limit of detection of 1 ng/mL for fentanyl/norfentanyl. The ARK II immunoassay has a 1 ng/mL cut-off for fentanyl and 7% cross-reactivity for norfentanyl; the Lin Zhi has a 5 ng/mL cut-off for norfentanyl and 131.58% cross reactivity for fentanyl. Results There were 9/129 discrepant samples between ARK II and Lin Zhi immunoassays as shown in Fig. 1. From the 59 confirmed samples Ark II resulted in one false positive sample and seven false negative samples (Fig. 1B) while the Lin Zhi assay resulted in 9 false negatives. Conclusion Given the current data set, there appear to be some discrepant results between the ARK II and Lin Zhi immunoassays. Most of the discrepant results observed have concentrations of fentanyl and norfentanyl that are close to the lower limit of immunoassay detection.