Before we begin: A blood alcohol level test measures the amount of alcohol in a sample of your blood. It may be used for legal or medical reasons. Learn more.
This tutorial walks you through everything you need to know about blood alcohol level. We explain it in plain language, step by step, so whether you are a student, a patient, or simply curious, you will come away with a solid understanding.
We cover what it is, why it matters, how it is diagnosed, and what you can do about it. Key facts are called out along the way.
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 alcohol. 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.
- Monitoringtreatment 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). The legal limit for BAC is usually 0.08%, but this limit is lower in certain states and for certain driver classifications. The effects of alcohol and your level of impairment increase as your BAC increases. Typical results are below.
- 0.01 to 0.05% BAC: You may feel relaxed, less alert, and have a slight loss of judgement.
- 0.06-.15% BAC: You may have slurred speech, reduced muscle coordination and impaired judgement, memory or balance.
- 0.16 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. You may experience gaps in memory (blackouts), vomiting or loss of consciousness.
- Over 0.31% BAC: Levels are 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 can detect alcohol in your system for up to about 12 hours after your last drink. Other factors can also affect your BAC and your level of impairment, including:
- Weight.
- Age.
- Sex.
- Type of alcohol.
- How quickly you drank.
- How much you ate before you drank.
- Medicines you’re taking.
- Sensitivity (tolerance) to alcohol.
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 check for alcohol use besides a breath or blood test.
- Hair. This test can show past alcohol use over a longer period.
- Urine. This test can check for recent alcohol use. Some urine tests can detect alcohol use over a longer time frame.
- Saliva. This method of testing is less common, but it can still be used to see if you’ve recently had an alcoholic drink.
- Sweat. This method of testing is also less common, but it can still be used to find traces of alcohol.
Also known as: blood alcohol level test, ethanol test, ethyl alcohol, blood alcohol content.
Key Takeaways
Understanding blood alcohol level is an important part of taking charge of your health. Here is what to remember:
- Know the signs — Recognizing early symptoms can lead to earlier diagnosis and better outcomes.
- Talk to your provider — If you have concerns or a family history of this condition, bring it up at your next checkup.
- Stay informed — Medical knowledge evolves. Keep learning and asking questions.
- You are not alone — Many people deal with this condition. Support groups and educational resources can help.