Comparison of the drug concentrations in oral fluid collected by two sampling methods (Varian OraLab and Statsure Saliva•Sampler)

Objective: To determine the influence of oral fluid sampling methods on drug concentrations. Methods: Oral fluid was obtained from 249 subjects by Varian OraLab and Statsure Saliva•Sampler. The OraLab consists of foam-tipped oral fluid collector. The sponge contains a salt that stimulates salivation. The Saliva•Sampler consists of a collector with a blue indication when 1 mL of oral fluid is collected. After sampling, the collector is transferred to a tube that contains 1 mL of buffer. Oral fluid was analysed for seven drugs with UPLC-MSMS. Results: For all the tested drugs, the concentrations in the oral fluid collected with OraLab were 37–76% compared to Statsure. Possible explanations are: a buffer and surfactants could explain a better extraction recovery with Statsure (particularly for THC) and the stimulation of salivation by a salt could explain lower concentrations in OraLab. A comparison of the concentrations in both samples showed a wide scatter with relatively low correlation coefficients (0.56–0.90). Conclusions: For all tested drugs, the concentrations measured in the oral fluid collected by OraLab are lower. This could have consequences for the determination of legal cut-offs