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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.
  • 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.
  • A person who drinks alcohol and takes certain medicines, such as antihistamines, sedatives (tranquilizers), or narcotics, 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.
  • Things 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.

Breath alcohol self-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. To learn more, see the topic Self-Test for Breath Alcohol.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

WebMD Medical Reference from Healthwise

Last Updated: November 07, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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