Paper: Detection of delta-9-tetrahydrocannabinol and cocaine derivatives in saliva samples: Impact of buccal cell content

French law requires roadside drug testing with an immunological kit, with positive results confirmed using oral fluid collected by a FLOQSwab® (FsW). However, this swab is designed for oral mucosa sampling, not for oral fluid collection. This study aimed to examine how buccal cell content, collected using FsW during roadside testing, affects the quantification of delta-9-tetrahydrocannabinol (THC), cocaine (C), and its metabolites (benzoylecgonine [BZE] and ecgonine methyl ester [EME])

Briefly, in the first step, a phosphate buffer was used to extract molecules from the swab. After ultrasound treatment, a homogenate was obtained. For the present works, we applied two treatments to this homogenate: either centrifugation, which produced a pellet (a dense sediment containing concentrated buccal cells), or compression of the FLOQSwab®, resulting in an extract product. THC, C, BZE, and EME were quantified at various stages of the protocol using a fully validated (ISO15189) liquid chromatography-mass spectrometry method. The limits of detection were 0.15 ng/mL for THC and 3 ng/mL for C, BZE and EME. In parallel, buccal cells were counted using a Malassez counting chamber in the homogenate and the pellet for the comparison of the different measurements.

A total of 150 Driving Under the Influence of Drugs (DUID) cases were analyzed for THC, along with 86 cases for cocaine and its metabolites. For THC, concentrations were consistently higher in the pellet, showing an average increase of 4.3-fold. Additionally, the pellet contained a mean of 3.5 times more cells than the homogenate. A significant positive correlation was also observed (R² = 0.79) between the number of buccal cells and the increase in concentration. In 5.3% of cases, THC was detected in the pellet but not in the homogenate. For cocaine, an average 1.4-fold increase in concentration was observed in the extract product in 43 out of 52 cases, with similar increases of 1.4 for BZE and 1.2 for EME. The extraction process identified 5 additional positive cases compared to the homogenate analysis, representing 9.6% of the samples.

A strong correlation between the number of buccal cells and THC concentration highlights their critical role in enabling detection, especially in cases where THC might otherwise remain undetectable. For cocaine and its metabolites, efficient compound extraction from swab fibers proved essential, increasing measurable concentrations and identifying additional cases. Tailored pretreatment methods are therefore fundamental for enhancing the sensitivity and reliability of oral fluid drug testing in DUID cases.