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

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.