About blood alcohol levels

Updated February 21, 2017

Blood alcohol levels are the most accurate way to find out how much alcohol is in the body. Its best known use is to determine the intoxication level of a driver, but it has other purposes. Blood alcohol levels register quickly, and various factors alter the results. If there's a car accident with injuries, usually the police demand a blood alcohol level test on all drivers.


There are several reasons for blood alcohol tests. It can pinpoint a drunken driver and absolve someone suspected of drunken driving. Sometimes, medical conditions such as hypoglycaemia or diabetes cause symptoms that imitate alcoholic confusion and unclear thinking. When a person is comatose, it helps eliminate the potential of an alcohol-induced coma. Police and program directors use it to find out whether people who are on programs for drug and alcohol abuse cheat. Occasionally, a child has a blood level alcohol test. This occurs when a child has alcohol poisoning from accidental ingestion or sipping too many adult drinks.


The blood alcohol level is from a test that measures the amount of alcohol in the blood. Because alcohol absorbs rapidly into the bloodstream, it only takes minutes to register a drink. Alcohol tends to peak in blood alcohol tests about an hour after the drink, but food in the system slows the absorption. The results show whether there's ethanol, which is alcohol, in the blood. If there's none, the test is normal.


Each state has different rules for the definition of legal intoxication. Many use the reading of .08 BAC (blood alcohol concentration) as the point where official intoxication begins for legal purposes. This is the recommended level from the National Highway Traffic Safety Administration.


The amount of alcohol in the blood varies by a person's size and other factors, even if you drink the same amount as a friend. For instance, a 54.4kg. woman might have two drinks in an hour and register a .08, official intoxication in most states. Her girlfriend might drink the same amount but weigh 63.5kg. and still be under the legal limit.


Gender makes a difference in blood alcohol tests. The same 54.4kg. woman who drank two alcoholic beverages and registered .08 would generally register .07 if she were a man. The difference comes from the amount of body fat. Women generally have more body fat than men, and alcohol doesn't go to the fat cells as easily and leaves more for the rest of the body. Hence, a woman weighing the same amount as a man would have less tissue that is non-fat and a higher concentration in that tissue.

Time Frame

The amount of drinks you have and your blood alcohol level also vary by the amount of time it takes for you to drink the beverages. If you had only three drinks for the evening but they were all at closing time, consider calling a cab. If, however, you spaced them over a 4-hour evening, the potential for a high blood alcohol level is limited.

Party Smart

Alcohol can be deadly in car accidents as well as from an overdose. The consensus is that .4 is the lethal blood alcohol level, but death may occur at even lower levels. The problem with alcohol poisoning is that there's no antidote, just treatment to keep a person alive while he displays symptoms. If you want to find out how high a few drinks takes your blood alcohol level, use the calculator in the Resources area.

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