B-273 Clinical Validation of a Novel Lateral Flow Assay for Rapid and Sensitive Urine Fentanyl Screening
Authors: Unsihuay Vila D , Butler W , Jannetto P , Xia X , Wang P 
Published: October 2024

Abstract

Background
The urgent need for rapid fentanyl detection at the point-of-care originates from its involvement in a high number of overdose deaths, primarily due to illicit use. Given fentanyl's potency compared to traditional opioids, accurate and sensitive detection is critical. Current lateral flow assays (LFA) cannot detect single-digit concentrations and may yield false negatives due to their lower sensitivity. Herein, we evaluate the clinical performance of a novel LFA (InstaStrip Fentanyl Rapid Test (urine)) with 1 ng/mL cutoff for fentanyl and no cross-reactivity for norfentanyl, offering enhanced sensitivity for effective overdose prevention at the ED.

Methods
A total of 172 urine samples submitted for UDS analysis were used for comparison studies. Fentanyl concentrations were categorized in 5 groups to cover various concentration categories around the cutoff of the LFA (1 ng/mL). These categories are: drug-free (&lt;0.1 ng/mL, n=68), 0.1-0.5 ng/mL (n=14), 0.5-0.9 ng/mL (n=15), 1-1.5 ng/mL (n=9) and &gt; 1.5 ng/mL (n= 66). Concentrations were determined by in-house LC-MS/MS methods validated according to CLIA standards, with fentanyl concentrations quantitated in the ABSciex software. For LFA testing, 150 μL of urine was added to a reagent tube containing dried rabbit anti-fentanyl antibody conjugated gold nanoparticles. After 20 sec of brief shaking, a test strip was inserted into the test tube. After 5 min, qualitative results were read as follow: both the control and test lines were visible in negative results, whereas only the control lines were visible in positive results. Method comparison study of the LFA was conducted by three operators who were blinded to the LC-MS/MS results. Result comparisons were made between the LFA strip and LC-MS/MS results, as well as among different operators for the same samples.

Results
Of the 75 urine samples with LC-MS/MS fentanyl concentrations ≥ 1 ng/mL, 74 produced consistently positive results using the InstaStrip Fentanyl Rapid Test. Of the 97 urine samples with LC-MS/MS fentanyl concentrations &lt; 1 ng/mL, 96 produced consistently negative results using the InstaStrip Fentanyl Rapid Test. Using the LC-MS/MS as the gold standard method and 1 ng/mL as a cutoff, the clinical sensitivity of InstaStrip Fentanyl Rapid Test was calculated to be 98.67% (95% confidence interval (CI) 92.79-99.97%), and the clinical specificity was 98.97% (95% CI 94.39-99.97%). Consistent results among three operators were obtained for 100% of the “drug free”, “0.1- 0.5 ng/mL” and &gt; 1.5 ng/mL groups, whereas 93.3 % (14 out of 15) and 88.9% (7 out of 8) were obtained for the “0.5-0.9 ng/mL” and “1-1.5 ng/mL” groups, respectively. The two samples with a singlet discrepant result (1 false positive and 1 false negative) in the triplicate experiments contained fentanyl concentrations of 0.9 and 1.0 ng/mL respectively, which are very close to the cutoff value.

Conclusions
In this study, the InstaStrip Fentanyl Rapid Test (urine) demonstrated high clinical sensitivity (98.67%), high specificity (98.97%) and high reproducibility showing that it may be useful in screening and identifying patients with fentanyl overdose in minutes in an emergency setting. This would facilitate appropriate patient triaging for optimal clinical care.