Medicolegal alcohol determination: comparison and consequences of breath and blood analysis

The concentration of alcohol in blood or breath has come to be regarded as the most objective indicator of impaired driving ability for medicolegal and other purposes. Regardless of the analytical method employed, there is substantial uncertainty about impaired driving ability at a particular alcohol concentration because of large differences in response among individuals to a given dose of alcohol. There is additional uncertainty associated with the particular analytical method used. Since breath alcohol analysis is the most common method employed for medicolegal purposes in the U.S., this method is compared to blood alcohol analysis in order to estimate its reliability and explore the numerous consequences resulting from the use of these methods. Results from blood and breath analyses are often used interchangeably, even though they are not necessarily equally valid indicators of impaired driving ability. To satisfy fundamental legal and scientific principles, it is concluded that the total uncertainty involved in a determination of impaired driving ability must be reported or otherwise accounted for in medicolegal applications.