Comparison of the DRI II and LZI I fentanyl immunoassays for in vitro clinical diagnostic use

Introduction Fentanyl, a highly potent synthetic opioid, has contributed to a rapid rise in opioid-related overdoses and fatalities nationwide. Consequently, the need for accurate and timely testing for fentanyl has become critical. Immunoassay screens, reported as presumptive positive or negative, help address this need. We sought to compare the clinical performance of 2 US Food and Drug Administration (FDA)–approved fentanyl immunoassays—the Thermo Scientific DRI Fentanyl II Drugs of Abuse Assay and the Lin-Zhi International LZI Fentanyl (Q) Enzyme Immunoassay—for detection of fentanyl and its metabolites in urine, using liquid chromatography–tandem mass spectrometry (LC-MS/MS) as the reference method. Methods A total of 806 urine specimens were screened using 2 FDA-approved fentanyl immunoassays on Beckman Coulter DxC 700 AU Chemistry Analyzer. Of these specimens, 183 that were both positive and negative by immunoassay were further analyzed by LC-MS/MS for the presence or absence of fentanyl, norfentanyl, and 4-anilino-N-phenethylpiperidine (4-ANPP). Results Of the 806 specimens, 786 (98%) provided concordant results and 20 (2%) had discordant results between the 2 immunoassays. Concordance between immunoassays and LC-MS/MS was 97% for the LZI assay and 89% for the DRI assay. Among the 183 specimens tested, 4-ANPP was detected in 13 (7%). Discussion The 2 assays demonstrated comparable clinical utility for incorporation into a urine drug screen panel.