What is a blood alcohol test?

A blood alcohol test measures the amount of alcohol in a sample of your blood. You will have alcohol in your blood if you've been drinking alcoholic beverages.

Alcohol is also called ethanol. It's the main ingredient of alcoholic drinks, such as beer, wine, and distilled spirits (liquor). When you have an alcoholic drink, the alcohol is quickly absorbed into your bloodstream. Your liver breaks down the alcohol so your body can get rid of it.

If you drink faster than your liver can break down alcohol, the alcohol level in your blood will increase and you may start to feel intoxicated (drunk). Alcohol intoxication affects how your brain works. At first, you may feel more relaxed, or talkative than usual. As alcohol levels increase, you may have some problems thinking clearly. You make have difficulty with your balance, slurred speech, slowed reaction time, and loss of judgement.

Continuing to drink after you are intoxicated can lead to an alcohol overdose. Symptoms include vomiting, trouble breathing, and passing out. An alcohol overdose can lead to coma or death.

There are a few blood tests that can measure whether a person has been drinking. A blood alcohol concentration (BAC) test is commonly used to see if a person has been drinking recently. It is also called a blood alcohol content test. This test can find alcohol in your blood for up to 12 hours after drinking. It can also show the amount of alcohol that you drank.

Other blood tests measure substances that may stay in your blood for weeks after you've had alcohol. These tests are typically used to test for alcohol use disorder (AUD) or to check whether a person recovering from AUD has stayed sober.

Other names: blood alcohol level test, ethanol test, ethyl alcohol, blood alcohol content

What is it used for?

A blood alcohol test may be used for many purposes, including:

• Legal evidence. Alcohol testing may be part of:
  • A check to see if you've been "driving while drunk." This means that your alcohol level is above the legal limit. To get quick results, police often ask you to breathe into a breathalyzer, a device that checks your breath for alcohol. But another option may be to go to a medical facility to get a blood test, which provides more accurate results than a breathalyzer.
  • A check for under-age drinking
  • An investigation into a criminal or motor vehicle accident investigation
  • A court case or as part of a parole agreement
• Employment. Employers test for alcohol use before hiring you. After you're hired, they may test you to check for on-the-job drinking. If you have a work accident, you may be tested to see whether alcohol was involved.
• Testing for alcohol poisoning. Hospital emergency staff may use a blood alcohol test to check for this life-threatening condition that can happen if blood alcohol level gets very high after drinking large amounts of alcohol. Young children can also get alcohol poisoning from drinking household products that contain alcohol, such as mouthwash and certain cold medicines.
• Monitoring treatment for alcohol use disorder. Some programs may require testing to see if you have been able to avoid drinking.

Why do I need a blood alcohol test?

You may need a blood alcohol test if you are suspected of drunk driving and/or have symptoms of intoxication. These include:

• Difficulty with balance and coordination
• Slurred speech
• Slowed reflexes
• Nausea and vomiting
• Mood changes
• Poor judgment

You or your child may also need this test if there are symptoms of alcohol poisoning. In addition to the above symptoms, alcohol poisoning can cause:

• Confusion
• Irregular breathing
• Seizures
• Low body temperature

What happens during a blood alcohol test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This process usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a blood alcohol test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Blood alcohol level results may be given in different ways, including percentage of blood alcohol content (BAC). Typical results are below.

• Sober: 0.0 percent BAC
• Legally intoxicated: .08 percent BAC
• Very impaired: .08–0.40 percent BAC. At this blood alcohol level, you may have difficulty walking and speaking. Other symptoms may include confusion, nausea, and drowsiness.
• At risk for serious complications: Above .40 percent BAC. At this blood alcohol level, you may be at risk for coma or death.

The timing of this test can affect the accuracy of the results. A blood alcohol test is only accurate within 6–12 hours after your last drink. If you have questions or concerns about your results, you may want to talk to a health care provider and/or a lawyer.

Learn more about laboratory tests, reference ranges, and understanding results.