Blood Alcohol

What To Think About

• The blood alcohol test measures only the amount of alcohol in the blood at the time the sample is taken. It does not show how long you have been drinking or whether you have an alcohol use problem.
• Highway patrol officers in most states now have devices (toximeters) that measure the breath alcohol levels of drivers they think are drunk. A person charged with drunken driving who does not think the breath analysis is accurate may ask for a blood alcohol test.
• A breath alcohol self-test can estimate your blood alcohol concentration. The handheld device to measure breath alcohol is similar to, though not as precise as, the type of test used by police for suspected drunk drivers. The breath alcohol self-test offers one piece of information to help you make a safe decision about drinking and driving. The safest decision is always not to drive if you have been drinking. For more information, see the medical test Self-Test for Breath Alcohol.
• The time that passes between drinking alcohol and collecting the blood or breath sample affects test results. The body continues to break down alcohol at a steady rate after drinking. So the amount of alcohol you drink can be estimated by knowing how much alcohol is present in your blood or breath and how much time has passed since you had a drink. In general, your body is able to break down about one drink per hour.
• Factors that affect how quickly the blood alcohol level rises in the body include:
  • The number of drinks per hour. As you increase the number of drinks per hour, your blood alcohol level steadily increases.
  • The strength of alcohol (proof or percentage) in the drink.
  • Your weight. The more you weigh, the more water is present in your body, which dilutes the alcohol and lowers the blood alcohol level.
  • Your sex. Women's bodies usually have less water and more fat than men's bodies. Alcohol does not go into fat cells as well as other cells, so women tend to keep more alcohol in their blood than men do. Also, a woman's hormones may affect the breakdown of alcohol.
  • Your age. One drink raises the blood alcohol level of an older adult more than it does for a young adult.
  • Eating. Food in the stomach absorbs some of the alcohol. The blood alcohol level will be higher if you do not eat before or during drinking.
  • The kind of mixer used. When carbonated mixers (such as tonic water or club soda) are used, the body absorbs alcohol more quickly.
  • Other medicines or drugs. A person who drinks alcohol and takes certain medicines, such as antihistamines or sedatives (tranquilizers), may feel more of the effects of alcohol. Also, a person who uses other drugs, such as marijuana, will feel the effects of both drugs more than if the drugs were used separately.

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Author:	Jeannette Curtis	Last Updated: May 9, 2008
Medical Review:	Kathleen Romito, MD - Family Medicine R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care, Medical Toxicology
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