Blood Alcohol Level

Why this test may be ordered

• To check if someone drove while above the legal BAC limit
• To test for alcohol use before hiring or after a work accident
• To check for alcohol poisoning in emergency situations
• To monitor treatment for alcohol use disorder

Preparation and collection

You don't need any special preparations for this test.

A health care professional will take a blood sample from a vein in your arm using a small needle. The process usually takes less than five minutes.

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.

Understanding results

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. The timing of this test can affect accuracy; a blood alcohol test can detect alcohol in your system for up to about 12 hours after your last drink. Other factors such as weight, age, sex, type of alcohol, how quickly you drank, how much you ate, medicines you're taking, and sensitivity to alcohol can also affect your BAC and level of impairment.

• 0.01 to 0.05% BAC: You may feel relaxed, less alert, and have a slight loss of judgement. Limitation: Individual effects vary based on factors like weight, age, sex, and tolerance. Next step: Discuss your results with a health care provider and/or a lawyer if you have questions or concerns.
• 0.06 to 0.15% BAC: You may have slurred speech, reduced muscle coordination, and impaired judgement, memory, or balance. Limitation: Individual effects vary based on factors like weight, age, sex, and tolerance. Next step: Discuss your results with a health care provider and/or a lawyer if you have questions or concerns.
• 0.16 to 0.30% BAC: 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. Limitation: Individual effects vary based on factors like weight, age, sex, and tolerance. Next step: Seek medical attention if you or someone else has severe symptoms such as confusion, irregular breathing, seizures, or low body temperature.
• 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. Limitation: Individual effects vary based on factors like weight, age, sex, and tolerance. Next step: This is a medical emergency. Call 911 or go to the nearest emergency room immediately.

• The timing of the test can affect accuracy; it can detect alcohol for up to about 12 hours after your last drink.
• Individual factors such as weight, age, sex, type of alcohol, how quickly you drank, how much you ate, medicines you're taking, and tolerance can affect your BAC and level of impairment.
• Results may be used for legal purposes; consult a lawyer if you have legal concerns.

What to do next

If you have questions or concerns about your results, talk to a health care provider and/or a lawyer.

• What do my blood alcohol level results mean for my health and safety?
• How do factors like my weight, age, and medications affect my BAC?
• What should I do if I or someone else shows signs of alcohol poisoning?
• How can I get help if I am concerned about my alcohol use?
• What are the legal implications of my BAC results?

Evidence source

U.S. National Library of Medicine: Blood Alcohol Level