Insights resulting from quantitative bioanalysis in studies of drugs and driving

In this study we examined the value of quantitative bioanalysis of drugs in studies on drugs and driving. Based on the fact that the use of psychoactive substances should not be combined with driving, one could argue that, especially for routine testing for driving under influence of drugs, reporting quantitative results is not necessary and that it is sufficient to determine the presence or absence of a drug (class) to study the prevalence of drugged driving or to estimate the crash risk. The example of alcohol, where crash risk is increasing exponentially with increasing blood alcohol concentrations (hence using a low cut-off for the presence of alcohol underestimates crash risk) suggests that using quantitative drug concentrations in bio-fluids might have added value. In the Belgian DUID-legislation both oral fluid and blood samples are taken and analysed with similar cut-offs. An objective of this thesis was to investigate the effect of using these similar cut-offs in paired samples of oral fluid and blood in a population of general drivers. For this purpose a dataset of almost 3000 paired samples was investigated. Quantitative analysis showed that 2.6 times more drivers confirmed positive in oral fluid compared to blood. Although the Belgian traffic law amendment (introducing both oral fluid screening and confirmation) went into force on October 1st, 2010, confirmation is still performed on blood samples but with lower cut-offs than before. To assess the influence of this change in enforcement procedure on the number of false positive screenings, two datasets of approximately 4000 positive screening cases each were compared. Quantitative analysis disclosed that fewer false positive screenings were observed since the implementation of the new legislation and that more recent drug use was targeted. The total number of positive screenings has dropped with the new legislation, but this is solely due to a lower number of positive screenings for cannabis, which can be explained by the much longer detection window of THCCOOH in urine (previous legislation) than THC in oral fluid (current legislation). Most risk estimations are calculated based on nominal categorisation (positive or negative) of the cases and controls. The concentration found in the biological matrices can also be of interest. We compared the distribution of plasma concentrations of several psychoactive substances between the general driving population (n= 2750) and seriously injured drivers (n= 377). Quantitative analysis illustrated that higher amphetamine and benzoylecgonine concentrations were found in injured drivers. In addition, a trend towards higher concentrations of benzodiazepines and Z-drugs was also observed. Accident risks should therefore also be assessed in relation to substance concentrations not only the presence or absence of a drug in a biological sample. Self-reporting is the most widely used method to measure prevalence of use of psychoactive substances. In the Belgian roadside study both questionnaire data and results of bioanalysis were collected. An objective of this thesis was to investigate the consistency between self-report and results of bioanalysis. Data on 2949 respondents providing questionnaire data and the results of bioanalysis of blood and/or oral fluid samples were investigated. Quantitative analysis revealed that the self-reported data underestimated the use of cannabis and that this underestimation was most obvious for recent use. Besides the fact that the DUID legislation requires quantitative bioanalysis of drug concentrations, quantitative bioanalysis is also of significant importance in epidemiological research on drug use and in research on accident risks associated with psychoactive substances.

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