Ethanol Analysis in Blood, Breath and Urine: Interpreting the Results

Abstract

Among a plethora of recreational drugs in common usage, none is more problematic for the individual and society than the legal drug ethanol, which is the psychoactive constituent in all alcoholic beverages. The analysis of ethanol in blood and other biological specimens is the most common request made to forensic science and toxicology laboratories, because drunken people are involved in many types of crime. After drinking alcoholic beverages, the ethanol they contain is rapidly absorbed into the bloodstream and transported throughout the body. Ethanol molecules easily cross the blood–brain barrier, depressing the central nervous system and slowing down brain activity. Both cognitive and psychomotor functions are impaired by excessive drinking in a dose-dependent manner in relation to the blood alcohol concentrations (BACs) reached. At low BACs (20–30 mg 100 mL−1), people tend to feel more relaxed and are less inhibited. As drinking continues to reach higher BACs (50–80 mg 100 mL−1), it takes longer to react in critical situations, judgement is impaired and people are more likely to take risks. Epidemiological surveys of drivers killed in road traffic crashes verify that 20–50% of the deceased had consumed alcohol before driving and that their BACs at autopsy were above the legal alcohol limit for driving. This chapter gives a general overview of the forensic aspects of ethanol with a main focus on its disposition and fate in the body, the concentrations determined in blood, breath and urine and how these should be interpreted in a legal context, such as when drunken drivers are prosecuted.