Assessing fitness to drive – proposal for a laboratory testing workflow tailored to the individual's case

Abstract

Aim

Violating the law on driving under the influence can lead to a forfeiture of the right to drive. Either before or after this temporary forfeiture the individual can be subject to an assessment of the fitness to drive. In Belgium, the latter can be executed by medical doctors. For what concerns the analytical tests executed during the assessments, there are no common procedures. This leads to differences in which tests are performed and in the associated costs for the individuals. Here we propose an analytical workflow, as followed in Ghent, which is tailored to the individual case.

Method

The individual is invited by the doctor for a medical assessment. During this assessment, the individual is questioned on his drinking behavior and on the use of drugs-of-abuse. Based on the background information that initially led to the invitation for the assessment and on the answers to the questions, a list of potential substances is drafted for which biological specimens will be tested. The biological specimens collected are urine, dried blood (collected via fingerprick) and a hair sample (maximum 5 cm is evaluated). If sample collection is not possible or refused, this is noted in the files. Samples are subject to different types of analysis: all urine samples are subject to a Nal Von Minden test and a screening based on liquid-chromatography high resolution mass-spectrometry (HRMS). If one of the screening methods indicates the presence of carboxy-THC, benzoylecgonine, amphetamines an/or opiates, the concentration is determined via other, independent, targeted MS-based methods. All dried whole blood samples are analyzed for their phosphatidylethanol 16: 0/18: 1 concentration (PEth). Hair samples are only tested for ethylglucuronide (hEtG) if PEth concentrations are below 270 ng/mL. Testing of hair for drugs-of-abuse is not performed when the urine tested positive for drugs of abuse. Hair testing for drugs (of abuse) is pursued in case of a negative urine test and if there are elements pointing at a (suspected) history of drug use.

Results

This workflow was evaluated based on 365 cases. In 56% of these, PEth and hEtG results were not in full agreement, which could be due to the differences in the window of detection. PEth has a shorter window of detection (several weeks) than hEtG (several months, depending on the length of the hair)–hence, if a subject recently changed drinking behavior, this would only be reflected in the PEth level. For example: 3 subjects with a PEth value < 20 ng/mL had hEtG ≥ 30 pg/mg. Based on the value of PEth these may have been considered fit to drive, but the hEtG level revealed excessive alcohol use in the months prior to testing.

A total of 163 samples was positive in the Nal Von Minden test. For the most commonly used drugs-of-abuse, this positive screening results could be confirmed by the HRMS screening and/or confirmatory targeted testing. Only for carboxy-THC, the positive Nal Von Minden test sometimes could not be confirmed (∼5% of cases)–for benzoylecgonine, on the other hand, the HRMS screening was positive in 8% of the samples that tested negative by the Nal Von Minden test, with cocaine use being confirmed via follow-up testing.

Conclusion

Performing the Nal Von Minden test in presence of the individual helps in opening a dialogue on substance use. The further cascade of screening and confirming the presence of biomarkers for drugs-of-abuse and ethanol intake allows an accurate picture of an individual's behavior, while limiting the number of hair analyses and targeted MS-based testing. This is beneficial for the efficiency of the testing process and minimizes the costs for the tested individuals.