Comparison of Oral Fluid and Urine for Detection of Fentanyl Use Using Liquid Chromatography with Tandem Mass Spectrometry

Abstract

Abstract Background We compared oral fluid (OF) and urine (UR) for detection of fentanyl (FEN) use in addiction medicine-psychiatry (AMP) clinics. Methods We measured FEN and norfentanyl (NRFEN) in UR with a limit of detection (LOD) of 2.0 µg/L and FEN in OF with an LOD of 0.5 µg/L by LC–MS/MS in 311 paired samples and compared the 2 matrices when higher OF and UR LODs were used. Results Urine (UR) detected more FEN use than OF using a LOD of 2.0 µg/L and 0.5 µg/L, respectively. FEN and/or NRFEN were detected in 44 and 59 UR specimens, respectively, and FEN in 46 OF specimens (43 OF+UR+, 3 OF+UR−, 16 OF−UR+, and 249 OF−UR−). In UR there were no instances with FEN positive and NORFEN negative. UR creatinine was <20 mg/dL in the 3 OF+UR− specimen pairs. The median OF/UR analyte concentration ratios in positive sample pairs were 0.23 for OF FEN/UR FEN and 0.02 for OF FEN/UR NRFEN. Conclusions We demonstrate that UR detects more FEN use than OF in an AMP setting when UR FEN and UR NORFEN LODs of 2.0 µg/L are used. OF is less sensitive than UR in detecting FEN use, but is still valuable for cases with low UR creatinine and/or suspected adulteration or substitution of UR. The UR vs OF comparison statistics are greatly impacted by even minimal adjustments of the LOD.