Validation of a lateral flow chromatographic immunoassay for the detection of fentanyl in drug samples

Background: Drug overdose deaths remain the primary cause of unintentional injuries in the United States. We examined the validity of a fentanyl test strip (FTS) in detecting fentanyl and its related analogs in water-based illicit drug solutions. Methods: Illicit drugs obtained from law enforcement (N = 343) were tested using a lateral flow chromatographic immunoassay FTS (BTNX Rapid Response) and Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) at a clinical chemistry laboratory in Baltimore, Maryland. Results: The FTS assay detected fentanyl at 200 ng/ml in water, and 13 additional fentanyl analogs, but failed to detect carfentanil and furanyl fentanyl at or below 1000 ng/ml. Overall sensitivity and specificity for detecting fentanyls was 98.5 % and 89.2 %; and the false negative and positive rate was 1.5 % and 10.9 %. False negatives (n = 2) occurred in fentanyl and a fentanyl precursor. False positives (n = 23) occurred in the presence of other illicit drugs and compounds (56.5 %) or when fentanyls were present below 40 ng/ml (43.5 %). False positive/negative rates remained low when testing cocaine and prescription opioid (PO) samples. Conclusions: FTS is a valid drug checking tool, however, rapid immunoassays and other drug checking instruments that can detect a wider range of fentanyl analogs including carfentanil need to be prioritized to minimize accidental exposure to the full spectrum of fentanyls.