The role of alcohol in U.S. traffic deaths may be substantially underreported on death certificates, according to a study in the Journal of Studies on Alcohol and Drugs.

Between 1999 and 2009, more than 450,000 Americans were killed in a traffic crashes. But in cases where alcohol was involved, death certificates frequently failed to list alcohol as a cause of death.

Injuries are the leading cause of death for Americans younger than 45, according to the Centers for Disease Control and Prevention. And it's important to have a clear idea of alcohol's role in those deaths, explained Ralph Hingson, Sc.D., of the U.S. National Institute on Alcohol Abuse and Alcoholism.

Hingson's team used a database maintained by the National Highway Traffic Safety Administration, called the Fatality Analysis Reporting System (FARS), which contains the blood alcohol levels of Americans killed in traffic crashes. They compared that information with death certificate data from all U.S. states. About half of U.S. states require that fatally injured drivers be tested for blood alcohol levels, and nationwide about 70% of those drivers are tested. Just 3 percent of death certificates listed alcohol as a contributing cause between 1999 and 2009. But FARS figures showed 21 percent of those deaths were legally drunk.

In some states—such as Maryland, Nevada, New Hampshire, and New Jersey—alcohol was rarely listed on death certificates. Certain other states did much better, including Delaware, Iowa, Kansas, and Minnesota. It's not fully clear why alcohol is so often left off of death certificates. One reason could be the time it takes to get blood-alcohol test results back. Coroners or medical examiners usually have to file a death certificate within three to five days, Hingson's team notes, but toxicology results might take longer than that.

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