Blood Alcohol Content (BAC)

Overview

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.

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 alcoholic drink per hour. One alcoholic 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:

  • 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 (alcohol abuse or alcoholism), 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.

Test Details

Who performs a blood alcohol content (BAC) test?

A healthcare provider called a phlebotomist usually performs blood draws, including those for a blood alcohol content test, but any healthcare provider who is trained in drawing blood can perform this task. A provider then sends the samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.

What should I expect during my blood alcohol content (BAC) test?

You can expect to experience the following during a blood test, or blood draw:

  • You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
  • Once they’ve located a vein, they’ll clean and disinfect the area.
  • They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
  • After they insert the needle, a small amount of blood will collect in a test tube.
  • Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
  • They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my blood alcohol content (BAC) test?

After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, the person or provider who ordered the test will share the results with you.

What are the risks of a blood alcohol content (BAC) test?

Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

When can I expect my blood alcohol content (BAC) test results?

Depending on the reason for the BAC test, you may receive your results within a few hours to several business days.

Results and Follow-Up

What do the results of a blood alcohol level (BAC) test mean?

Your report may provide blood alcohol level test results in different ways depending on the laboratory that processes the test. The results are typically reported in the percentage of blood alcohol content (BAC) — for example, 0.03% BAC. They can also be listed as grams per milliliter (g/mL). This test result would be 0.03 g/100 mL.

The results may also indicate “positive” or “negative,” meaning you did have alcohol in your blood or you had no alcohol in your blood, respectively.

The timing of a BAC test can affect the accuracy of the results. A blood alcohol test is only accurate within six to 12 hours after your last alcoholic drink. If you have questions or concerns about your results, talk to your healthcare provider and/or a lawyer, depending on your situation.

Frequently Asked Questions

For most states in the United States, the alcohol limit to legally drive a vehicle for drivers aged 21 or older is currently 0.08% BAC. Utah’s legal limit is lower, at 0.05% BAC. Like all laws, these legal limits can change.

A note from Cleveland Clinic

In moderation, alcohol can be OK for people old enough to legally drink. However, if you drink excessive amounts of alcohol in a short amount of time and/or drink large amounts frequently, your health can be at risk. If you’re concerned about your drinking habits, reach out to your healthcare provider or a specialist. Together, you can come up with a plan to improve your habits and health.

Last reviewed by a Cleveland Clinic medical professional on 04/11/2022.

References

  • Centers for Disease Control and Prevention. Alcohol and Public Health. (https://www.cdc.gov/alcohol/faqs.htm) Accessed 4/11/2022.
  • MedlinePlus. Blood Alcohol Level. (https://medlineplus.gov/lab-tests/blood-alcohol-level/) Accessed 4/11/2022.

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