Comparison of urine and hair testing for drugs of abuse in the control of abstinence in driver's license re-granting.

The purpose of the study was to compare the detection rate of illicit drugs in urine and hair specimens. The samples were taken from subjects trying to regain their revoked driver's license after a drug- or alcohol-related traffic offence. In 2010, we screened 14 000 urine and 3900 hair samples for amphetamines, methamphetamines, cannabinoids, cocaine, opiates, methadone, and benzodiazepines as well as for ethylglucuronide. We used the low threshold values of the new German guidelines for Medical Psychological Assessment (MPA). Positive screening tests were confirmed with gas chromatography-mass spectrometry (GC-MS), gas chromatography-tandem mass spectrometry (GC-MS/MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that positivity rates for methamphetamines, MDMA, cocaine, and monoacetylmorphine were 1.7-, 5.7-, 3.8- and 9.3-fold higher in hair than in urine. In contrast, the detection rate for benzodiazepines was higher in urine than in hair (oxazepam, 0.21% versus 0%, nordiazepam 0.10% versus 0.03%). The positivity rate in hair for ethylglucuronide was 6-fold (12.7%) that for urine testing (2.1%). The study reveals that in the control of abstinence in the context of driving license re-granting there are in part large differences of positivity rates for some drugs or metabolites between hair and urine samples. These differences should be kept in mind by physicians and psychologists in traffic medicine who are ordering the drug testing.