B-319 Evaluation of A Test Strip for Rapid Detection of Fentanyl

Background Rapid detection of fentanyl or fentanyl analogues in samples from patients who knowingly or unknowingly use analgesia or street drugs can help save lives. In doctor’s offices or in the hands of first responders, point-of-care devices are needed to detect fentanyl. We have evaluated a fentanyl test strip using urine samples and determined the cutoff, sensitivity and specificity for fentanyl using liquid chromatography tandem mass spectrometry (LC/MS/MS) as a comparator. Methods One hundred and eighty-seven residual urine samples from inpatients or patients presented to the emergency department at Ronald Reagan Hospital were used in the study. Fentanyl was tested with the One Step Fentanyl Test Strip (W.H.P.M., Inc., Irwindale, CA), which returns qualitative results. The One Step Fentanyl Test Strip (Strip) is a lateral flow test strip based on competitive immunoassay principle, that comprises a sample pad, a reagent pad with labeled anti-fentanyl antibody, a testing zone that has a test line and a control line, and an absorbance pad at the other end of the strip. When dipped in a sample, fluid will flow from the sample pad to the reagent pad due to capillary actions, carrying the reagent to the testing zone. The test line will be visible if fentanyl concentration in a sample is lower than the cutoff of the strip, indicating a negative result. Vice versa, the test line will not show up if the concentration of fentanyl in a sample is higher than the cutoff of the strip, indicating a positive result. The concentration of fentanyl and norfentanyl in these 187 urine samples were measured with a method using LC/MS/MS at UCLA Olympic Analytical Laboratory and results were considered positive if the concentration of either fentanyl or norfentanyl is greater than or equal to 1.0 ng/mL. Results The concordance and discordance between the strip and LC/MS/MS were given in Table 1. Comparing to LC/MS/MS, the sensitivity of the strip was 100% (134/134), and the specificity was 84.9% (45/53). The positive and negative predictive value of the strip was 94.4% and 100%, respectively. The cutoff of the strip is determined to be 1 ng/mL based on receiver operating characteristic (ROC) curve (data not shown). Conclusion The strip has a high sensitivity (100%) for fentanyl with a cutoff of 1 ng/mL, which is very sensitive for screening fentanyl in urine samples. The relatively lower specificity (84.9%) is probably caused by some other fentanyl analogues present in some samples that were not measured by LC/MS/MS or could be due to the defect of the strip that did not make the test line show up clearly. Because sensitivity is most important for screening methods, the performance of the strip is acceptable for point of care testing for fentanyl.