B-292 Performance of fentanyl immunoassays in a pediatric patient population

Background Exposure to the synthetic opioid fentanyl continues to incite the opioid epidemic in the United States. Mirroring adults, fentanyl poisonings amongst pediatric patients continue to rise. A urine toxicology screen may be considered for all children presenting with altered mental status and neurologic symptoms. The Fentanyl II Enzyme Immunoassay from Roche (FEN2) and ARK Fentanyl II Assay by ARK Diagnostics (ARK II) are FDA-approved immunoassays designed to respectively detect the presence of norfentanyl and fentanyl in urine. Their efficacy in screening fentanyl exposure within pediatric populations remains unstudied. We describe validations of the FEN2 and ARK II assays and evaluate their potential addition to the immunoassay-based urine toxicology screening panel within our pediatric hospital setting. Methods Performance of the FEN2 (5 ng/mL norfentanyl cut-off) and ARK II (1 ng/mL fentanyl cut-off) assays were determined through an assessment of assay precision, accuracy, linearity, cross-reactivity with related analytes, carryover and ability to detect low concentrations of norfentanyl in urine. All FEN2 and ARK II discrepant screening results were evaluated by liquid chromatography tandem mass spectrometry (LC-MS/MS) confirmation testing. De-identified, remnant urine specimens (N=125) submitted for urine toxicology screening were also tested using the FEN2 and ARK II immunoassays. Results Intra- and inter-day imprecision for the FEN2 and ARK II assays were comparable (<9%). The FEN2 and ARK II manufacturer cross-reactivity claims for fentanyl (3.8 and 1.0 ng/mL) and norfentanyl (5.0 and 15.0 ng/mL) were verified respectively. However, the ARK II assay response from urine spiked with norfentanyl only (50 to 1,000 ng/mL) was consistently near the cut-off (94 to 96% cross-reactivity). FEN2 and ARK II respectively showed a 100% and 96.4% concordance with LC-MS/MS. Only FEN2 accurately identified a positive specimen with 0 ng/mL fentanyl and 6.4 ng/mL norfentanyl. Both assays produced accurate qualitative screening results from archived College of American Pathology (CAP) proficiency testing material. No carryover was observed at 10,000 ng/mL fentanyl and norfentanyl. All de-identified remnant urine specimens screened negative on both fentanyl assays (100% concordance). Conclusion The FEN2 and ARK II were evaluated to have similar analytical performance and are suitable for pediatric use. FEN2 exhibited higher clinical sensitivity. Clinicians have requested this test due to the growing cases of pediatric fentanyl exposure. Including fentanyl testing in routine urine toxicology screening panels can identify potential toxicology etiologies earlier and negate further diagnostic procedures.