Driving after illicit drug use is a worldwide growing concern requiring rapid and sensitive screening at the roadside. It is noteworthy that the sampling method used to collect oral fluid (OF) may significantly influence drug concentrations in the collected sample and thus alter the accuracy of the measurement. We evaluated two OF collection devices, Quantisal and Certus collectors, for their suitability for collecting samples to allow laboratory confirmation of driving after illicit drug use. Four parameters were studied including (i) the collected OF volume; (ii) the recovery efficiency using OFs spiked with opiates, cannabinoids, amphetamines, cocaine and its metabolites; (iii) drug stability after storage for 1, 7 and 14 days at -20°C, +4°C and room temperature; and (iv) the impact of mouth cells present in the collected OF on drug stability. Drug concentrations were measured using gas and liquid chromatography-mass spectrometry. Certus collector allowed the collection of significantly larger (0.94 ± 0.18 mL vs. 0.84 ± 0.06 mL, P = 0.08) but less reproducible OF volumes (19 vs. 6.7%) compared with Quantisal collector. Drug recovery was significantly better with Quantisal than with Certus collector, especially when used to detect cannabinoids (0.94 vs. 0.54, P < 0.001 for ∆9-tetrahydrocannabinol (THC)). For both OF collectors, storage at 4°C was preferable except for methadone, the stability of which was altered by adherence to the collector device. In the presence of mouth cells in the OF sample, THC concentrations were significantly decreased at Day 7 in comparison with Day 1 with both collection devices (P = 0.001 with Quantisal collector and P = 0.01 with Certus collector). In conclusion, Quantisal collector is more reliable than Certus collector although the practicability of both devices remains to be determined at the roadside.

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