B-307 Comparing Urinary Fentanyl Levels Among Hospital Patient Groups

Background Fentanyl continues to be a major public health challenge in the United States, despite extensive educational efforts aimed at mitigating its impact. Typically, urine concentrations of fentanyl are not commonly employed as quantitative markers for clinical decision-making, but they provide a useful surrogate for understanding population-level exposure. In this study, we used both immunoassays and high-resolution mass spectrometry to detect fentanyl and xylazine, then these sample were quantified by an in-house LC-MS/MS method, to explore concentrations across five distinct populations. Methods The five groups are as followed opiate treatment outpatient program (OTOP), comprehensive drug screen high resolution mass spectrometer (CDHR) group which includes any patient who`s attendee requested the in-house comprehensive drug screen to evaluate a patient`s presentation, emergency department (ED), outpatient clinics, and special clinics which include locations like HIV, TB, gender affirming etc. Urine samples were collected between February 2024 and January 2025. A total of 278 samples were analyzed. All samples underwent processing using an in-house developed LC-MS/MS method designed to detect fentanyl, norfentanyl, and xylazine. The resulting data was analyzed in R, using Wilcoxon rank-sum testing and Kolmogorov-Smirnov (KS) tests to look at central tendency and distribution differences. Results The analysis revealed one cohort who had significantly different concentrations in fentanyl, norfentanyl, and xylazine. OTOP patients had notably higher fentanyl concentrations (Median = 1.49 µg/mL, Max = 37.02 µg/mL) compared to all other groups. Similarly, norfentanyl levels (Median = 5.50 µg/mL, Max = 96.22 µg/mL) were elevated in this cohort. The interquartile range (IQR) for norfentanyl was the highest of the three components, suggesting substantial variability in metabolism or exposure, regardless of opioid use history. Wilcoxon rank-sum testing confirmed significantly higher fentanyl levels in OTOP compared to the ED (p < 1.18e-12), while no significant differences were found among the non-OTOP groups. Kolmogorov-Smirnov (KS) testing indicated distinct concentration distributions in OTOP (p < 0.0001), with differences observed between CDHR and ED. Xylazine was detected across all patient groups, but its concentrations remained consistently low, with median levels =0.03 µg/mL and many values in the ng/mL range. The highest observed xylazine concentration was 1.43 µg/mL in OTOP, but most samples had values well below 0.1 µg/mL. Conclusion Fentanyl concentrations in urine samples have a wide dynamic range, but a clear distinction in people who use heavily. Based on the analysis of over 278 samples, it was concluded that an upper detection limit of 13 µg/mL would effectively cover more than 95% of patients. However, norfentanyl concentrations were observed to exceed this threshold in some cases, reaching as high as 35 µg/mL, with a upper limit of coverage placed at 25 µg/mL. Additionally, while xylazine was detected in the population, its concentrations were notably lower than fentanyl, typically below 1 µg/mL, with many samples in the ng/mL range. These findings demonstrate fentanyl exposure in different clinical contexts