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Blood Alcohol Concentration (BAC)

Blood alcohol concentration (BAC) is the amount of alcohol in the bloodstream. It is measured in percentages. For instance, having a BAC of 0.10 percent means that a person has one part alcohol per 1,000 parts blood in the body.

In a review of studies of alcohol-related automobile accidents, it was found that reaction time, tracking ability, concentrated attention ability, divided attention performance, information-processing capability, visual function, perceptions, and psychomotor performance were all significantly impaired at a BAC of 0.05 percent. Impairment first appeared in many of these important areas of performance at a BAC of 0.02 percent, which is substantially below the legal standard in most states for drunkenness, 0.10 percent.

Approximately half of traffic injuries involve alcohol. About one-third of fatally injured passengers and pedestrians have elevated blood alcohol levels. For fatal intentional injuries, half of all homicides involve alcohol, as do one-quarter to one-third of suicides.

The Centers for Disease Control and Prevention (CDC) estimate that about 30,000 unintentional injury deaths per year are directly attributable to alcohol. In addition, 15,000 to 20,000 homicides/suicides per year are associated with alcohol.

BAC can be measured by breath, blood, or urine tests. BAC measurement is especially important for determining the role of alcohol in crashes, falls, fires, crimes, family violence, suicide, and other forms of intentional and unintentional injury. Information on BAC:

  1. provides a baseline for evaluating prevention and intervention programs
  2. supplies data needed for planning and providing services
  3. improves estimates of the economic costs of alcohol use

One problem in obtaining accurate BAC data is a lack of testing in hospital emergency rooms. Research indicates that emergency rooms do not test routinely for alcohol in crash victims. A national survey of trauma centers found that although two-thirds of the centers estimated that the majority of patients had consumed alcohol, only 55 percent routinely conducted BAC tests at patient admission. A review of emergency room studies indicated that up to one-third of patients admitted to emergency rooms are not tested for alcohol consumption.

The public most commonly associates BAC with drunk driving. However, it is more accurate to use the term "alcohol-impaired driving" because one need not be drunk (intoxicated) to be demonstrably impaired. Driving skills, especially judgment, are impaired in most people long before they exhibit visible signs of drunkenness. While most states define legal intoxication for driving purposes at a BAC of 0.10 percent or higher, alcohol may cause deterioration of driving skills at 0.05 percent or even lower. Deterioration progresses rapidly with rising BAC.

Source: Prevention Primer, Center for Substance Abuse Prevention.