Comparison between blood analysis and police assessment of drug and alcohol use by injured drivers.

Official statistics for alcohol/drug use by drivers can influence the introduction of intervention measures against impaired driving. Thus, the validity of official statistics is important. Since official statistics are based on police assessment of inebriation, the present study was aimed at investigating this issue by comparing blood analysis with the rate of police detection of alcohol/drug use by injured drivers. All injured motor vehicle drivers who were hospitalized (HD) (Umeå: n = 104) and all fatally-injured drivers (FD) who were autopsied (Umeå, Northern Sweden: n = 110; Gothenburg, Western Sweden: n = 133) from May 1991 through Dec 1993 were tested for alcohol and both licit and illicit drugs. The findings of the blood analyses were compared with police assessment of inebriation. In the HD, the police suspected inebriation in 13% (n = 13) whilst blood analyses showed drug and or alcohol in 18% (n = 19) of the drivers (sensitivity 69%; specificity 97%). In the FD, the police suspected inebriation in 7% (n = 16) of the drivers whilst blood analyses showed drug and/or alcohol in 23% (n = 57) of the drivers (sensitivity 53%; specificity 100%). The blood alcohol-positive HD who the police suspected to be inebriated had significantly higher mean blood alcohol concentrations than those not suspected. To avoid biased statistics, official statistics on inebriation of injured drivers should be based on blood analysis of drug/alcohol and not on police assessment.