Blood Alcohol Content (BAC): What It Is & Levels - Cleveland Clinic

What is blood alcohol content (BAC)?

Blood alcohol content (BAC), also known as a blood alcohol level, is the amount of alcohol in your blood.

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Alcohol (ethyl alcohol or ethanol) is the intoxicating ingredient found in beer, wine and liquor. When you drink a beverage that contains alcohol, your stomach and small intestines rapidly absorb the alcohol and enter it into your bloodstream. Alcohol is a toxin to your body, so your liver then metabolizes the alcohol to filter it out of your blood.

If you’re drinking faster than your liver can process the alcohol, your BAC increases and you may feel the effects of drunkenness, also called intoxication. In general, your liver can process about one alcohol-containing drink per hour. One drink is typically defined as 12 ounces of beer, 5 ounces of wine or 1.5 ounces of liquor. However, different beers and wines can contain different percentages of alcohol.

The amount of alcohol in your blood can vary based on several factors including:

• The amount of alcohol you’re drinking.
• How quickly you’re drinking.
• How much food you ate before drinking.
• Your age and weight.

What do different blood alcohol levels indicate?

Alcohol is a central nervous system depressant (it reduces stimulation in your central nervous system) and affects every organ in your body.

Here’s how different percentages of blood alcohol content (BAC) can affect you physically and mentally:

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• BAC 0.0%: There’s no alcohol in your blood (you’re sober).
• BAC 0.02%: At this percentage, you may experience an altered mood, relaxation and a slight loss of judgment.
• BAC 0.05%: At this percentage, you may feel uninhibited and have lowered alertness and impaired judgment.
• BAC 0.08%: At this percentage, you may have reduced muscle coordination, find it more difficult to detect danger and have impaired judgment and reasoning.
• BAC 0.10%: At this percentage, you may have a reduced reaction time, slurred speech and slowed thinking.
• BAC 0.15%: At this percentage, you may experience an altered mood, nausea and vomiting and loss of balance and some muscle control.
• BAC 0.15% to 0.30%: In this percentage range, you may experience confusion, vomiting and drowsiness.
• BAC 0.30% to 0.40%: In this percentage range, you’ll likely have alcohol poisoning, a potentially life-threatening condition, and experience loss of consciousness.
• BAC Over 0.40%: This is a potentially fatal blood alcohol level. You’re at risk of coma and death from respiratory arrest (absence of breathing).

Some people can develop a tolerance to alcohol. This means that they may not feel the same physical and mental effects of alcohol drinking the same amount they used to drink. This doesn’t mean their blood alcohol content (BAC) is lower. It just means they experience the effects of alcohol differently.

When would I need a blood alcohol content (BAC) test?

People have BAC tests for a variety of reasons, including:

• Medical testing: Healthcare providers use BAC tests for diagnosing alcohol poisoning, a potentially life-threatening complication of consuming excessive amounts of alcohol in a short amount of time.
• Monitoring alcohol use disorder: If you’re in a treatment program for alcohol use disorder, they may have you undergo BAC tests while you’re in the program to see if you’re continuing to drink alcohol while in recovery.
• Workplace testing: Your employer may test for alcohol use if you’re a new applicant, regularly during employment and/or after an accident on the job.
• Legal testing: People may need to undergo a BAC test as a part of a legal investigation, such as in the case of underage drinking, monitoring for alcohol use while on parole and determining if a person is/was driving a vehicle while legally intoxicated.