Impact of buccal cell content and swab retention on tetrahydrocannabinol and cocaine concentrations in oral fluid.

Saint-Marcoux F.; Campos Lapa N.; Dulaurent S.; Griffeuille P.; El Balkhi S. · Journal of analytical toxicology · 2026

**Background & Methods** This analytical study investigated how buccal cell content and sample fractionation affect drug detection in oral fluid specimens collected using FLOQSwabs®. Oral fluid samples (n=102 for THC; n=52 for cocaine analytes) were processed through elution, sonication, and vortex mixing, with three fractions analyzed separately (homogenate, cell-rich pellet, and expressed swab) using LC-MS/MS to measure THC, cocaine, benzoylecgonine (BZE), and ecgonine methyl ester (EME) concentrations. **Key Findings** • **THC shows cell-dependent distribution**: Median buccal epithelial cell counts and THC concentrations were significantly higher in the cell-rich pellet compared to homogenate (p<0.001), with median enrichment ratios of 4.40 and 3.93 respectively. A strong to very strong correlation (r=0.77–0.88) existed between cellular enrichment and THC enrichment for concentrations above 5 ng/mL. Four specimens were below detection limit in homogenate but detectable in the pellet, suggesting buccal cells serve as a THC reservoir. • **Cocaine analytes show swab-dependent distribution**: Unlike THC, cocaine and its metabolites demonstrated comparable concentrations between homogenate and pellet fractions. The expressed swab fraction consistently yielded the highest analyte levels, with median expressed swab-to-homogenate ratios of 1.16 (cocaine), 1.28 (BZE), and 1.14 (EME), indicating incomplete release of cocaine-related compounds from the collection device. • **Pre-analytical effects are analyte-dependent**: Results demonstrate that different drugs are affected by distinct pre-analytical variables—buccal cells act as a reservoir specifically for THC, while cocaine-related analytes are primarily influenced by incomplete swab release, introducing significant variability in oral-fluid measurements. **Dosage & Administration** Not reported. **Safety & Adverse Effects** Not reported. **Evidence Quality** This is an analytical validation study with moderate evidence quality. Limitations include reliance on a single collection device (FLOQSwabs®), which may limit generalizability to other oral fluid collection methods. The study lacks information on participant demographics, timing of drug use, or clinical outcomes. However, the consistent methodology, adequate sample sizes for THC analysis, LC-MS/MS analytical rigor, and statistically significant findings strengthen the evidence. These results have important implications for standardizing oral fluid collection and interpretation in forensic and roadside toxicology, though further validation across diverse populations and collection devices is warranted.

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