Health Information and Tools > Patient Care Handouts >  Blood Alcohol Test: About This Test
Facebook Tweet Email Share

Main Content

Blood Alcohol Test: About This Test

What is it?

A blood alcohol test measures the amount of alcohol in the body. This measurement is called the blood alcohol concentration, or BAC.

The blood alcohol test measures only the amount of alcohol in the blood at the time the sample is taken. It does not show how long you've been drinking or whether you have an alcohol-use problem.

Why is this test done?

A test for blood alcohol level is done to:

  • Check the amount of alcohol in the blood if you are suspected of being legally drunk.
  • Find the cause of an altered state of mind, such as unclear thinking, confusion, or coma.

What happens during the test?

A health professional takes a sample of your blood.

What else should you know about the test?

  • How much alcohol makes you legally drunk (too drunk to drive) varies among provinces.
  • If alcohol is found in your blood, the BAC can range from very little, such as a BAC of 0.02, to a BAC of more than 0.50. A BAC of 0.50 is very high and can cause death.
  • Your blood alcohol concentration depends on many things, including your age, your size, whether you are male or female, and whether you have recently eaten. Here are some examples of BAC and its effect:
    • 0.05: Slowed reaction time
    • 0.10: Slurred speech
    • 0.20: Hard to walk, nausea, vomiting
    • 0.40: Possible coma and death

What happens after the test?

  • The doctor will give you information on how to help yourself when you get home.

When should you call for help?

Call 911 anytime you think you may need emergency care. For example, call if:

  • You are very confused or can't think clearly.
  • You are thinking about killing yourself or about hurting others.
  • You have a seizure.
  • You vomit blood or what looks like coffee grounds.

Call your doctor or nurse call line now or seek immediate medical care if:

  • You have new or worse symptoms of withdrawal, such as trembling, feeling restless, and sweating.
  • Your withdrawal symptoms come back after not bothering you for days or weeks.
  • You cannot stop vomiting.

Watch closely for changes in your health, and be sure to contact your doctor or nurse call line if:

  • You need help to stop drinking.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

Go to

Enter B433 in the search box to learn more about "Blood Alcohol Test: About This Test".

Care instructions adapted under license by your healthcare professional. If you have questions about a medical condition or this instruction, always ask your healthcare professional. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.