What is a blood alcohol test?

A blood alcohol test measures the amount of alcohol (also called ethanol) in a sample of your blood. Alcohol is the ingredient in beer, wine, and distilled spirits (liquor) that makes you feel intoxicated (drunk).

When you have an alcoholic drink, your digestive tract quickly absorbs the alcohol. It then enters your bloodstream and stays there until your liver can break it down and filter it out of your blood. Your liver needs time to do this. If you consume alcohol faster than your liver can get rid of it, your blood alcohol levels will rise. The higher these levels rise, the more intoxicated you'll feel.

There are a few blood tests that can measure whether a person has been drinking. The most common is the blood alcohol concentration/content (BAC) test. This test shows the amount of alcohol in your blood for up to 12 hours after drinking.

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 is most often used to determine not only if alcohol is present in your blood but also to what extent it's affecting you. Alcohol can change various brain functions. If you've only consumed a small amount, these changes aren't often dangerous to your immediate health. Your mood might change, and your reaction time may be reduced. Larger amounts of alcohol, however, can be much more dangerous, leading to coma or even death.

You may need to take a blood alcohol test for a number of reasons, including:

• Legal evidence. Law officials may use BAC tests to see if someone drank while underage, broke a parole agreement, or drove while above the legal BAC limit. For quick results, a police officer may use a breathalyzer, a device that checks your breath for alcohol. Or they may bring you to a medical facility to get a blood test, which can provide a more accurate reading of your BAC.
• Employment. Your employer may test for alcohol use before hiring you. After you're hired, they may also test you to see if you're under the influence of alcohol while on the job, especially if you're ever involved in a work accident.
• Testing for alcohol poisoning. Hospital emergency staff may use a blood alcohol test to check for this life-threatening condition that can happen if your blood alcohol level gets dangerously high from drinking 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.

• 0.0% BAC: You're sober. There is no alcohol in your blood.
• 0.1 to 0.7% BAC: There is alcohol in your blood, but your levels are below the legal limit. You may feel relaxed, less alert, and have a slight loss of judgement.
• 0.8% BAC: This is the limit for legal intoxication. Driving at this BAC level or higher is illegal and dangerous. You may have reduced muscle coordination and impaired judgement.
• 0.10 to 0.30% BAC: In this range, you will feel more serious signs of intoxication such as difficulty walking and speaking. You may also feel drowsy, confused, and nauseated.
• Over 0.30% BAC: You'll likely have alcohol poisoning with this much alcohol in your blood. Above 0.40% BAC is especially dangerous and may even be fatal. You may lose consciousness, have trouble breathing, or go into a coma.

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. Other factors can also affect your BAC, including:

• Weight.
• Age.
• Sex.
• Type of alcohol.
• How quickly you drank.
• How much you ate before you drank.

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.

Is there anything else I need to know about a blood alcohol test?

Some employers or legal officials may rely on other methods to test your blood alcohol level. They may check your:

• Hair. This test can see if you've had an alcoholic drink within the past 10 days.
• Urine. This test can see if you've had an alcoholic drink within the past 5 days.
• Saliva. This method of testing is less common, but it can still be used to see if you've had an alcoholic drink within the past 6 to 12 hours.
• Sweat. This method of testing is also less common, but it can still be used to find traces of alcohol in your blood.