The objective of this study was to compare the number of drivers with drug concentrations above the legal cutoffs for driving under the influence of illicit substances in paired samples of blood and oral fluid. Between January 2008 and September 2009, 2,949 randomly selected drivers participated in a roadside survey. Each was asked to provide blood and oral fluid. Samples were analyzed for 11 illicit substances or metabolites by ultra-performance liquid chromatography-tandem mass spectrometry and gas chromatography-tandem mass spectrometry. Out of the 2,750 drivers who gave both blood and oral fluid, 28 (1.0%) had drug concentrations above the legal cutoff in blood and 71 (2.6%) were above the legal cutoff in oral fluid. Fifteen (7.5%) of the 199 drivers who gave an oral fluid sample but refused to provide blood tested positive, significantly more than drivers who provided both samples. Based on oral fluid analysis, 2.6 times more subjects tested positive for drugs compared to blood analysis. Those that refused to give a blood sample were 3 times more likely to test positive for drugs. Even in a survey that guaranteed total anonymity, people fearing a positive test result might have been more likely to refuse to give a blood sample.

The objective of this study was to compare the number of drivers who self-reported cannabis use by questionnaires to the results of toxicological analysis. During roadside surveys, 2957 respondents driving a personal car or van completed a questionnaire to report their use of drugs and medicines during the previous two weeks and to indicate the time of their last intake. Cannabis was analyzed in oral fluid by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), in blood by gas chromatography-mass spectrometry (GC-MS). Frequencies in the time categories were calculated and compared with toxicological results. Diagnostic values were calculated for the time categories in which positive findings were to be expected (<4 h and <2 4h, respectively for tetrahydrocannabinol (THC) and delta9-tetrahydrocannabinol (THCCOOH) in blood, <12 h for THC in oral fluid). Most self-reported cannabis use was more than 12 h before driving. The sensitivity of the questionnaire was low, while the specificity and accuracy were high. Kappa statistics revealed a fair agreement between self-report and positive findings for THC in oral fluid and blood and moderate agreement with THCCOOH in blood. Self-report largely underestimates driving under the influence of cannabis, particularly recent cannabis use; therefore analysis of biological samples is necessary.

A high percentage of the injured drivers were positive for a psychoactive substance at the time of injury. Alcohol was the most common substance, with 80 percent of the positive drivers having a BAC ≥0.5 g/L. Compared to a roadside survey in the same area, drivers/riders with high BACs and combinations of drugs were overrepresented. Efforts should be made to increase alcohol and drug enforcement. The introduction of a categorization and labeling system might reduce driving under the influence of medicinal drugs by informing health care professionals and patients.

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Evaluative conditioning refers to the observation that the mere pairedpresentation of a neutral stimulus (CS) with a liked or disliked stimulus (US) may result in the neutral