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A blood alcohol test measures the amount of alcohol (ethanol) in your body. Alcohol is quickly absorbed into the blood and can be measured within minutes of having an alcoholic drink. The amount of alcohol in the blood reaches its highest level about an hour after drinking. But food in the stomach may increase the amount of time it takes for the blood alcohol to reach its highest level. About 90% of alcohol is broken down in the liver. The rest of it is passed out of the body in urine and your exhaled breath.
Alcohol has a noticeable effect on the body, even when consumed in small amounts. In large amounts, alcohol acts as a sedative and depresses the central nervous system.
A blood alcohol test is often used to find out whether you are legally drunk or intoxicated. If this test is being done for legal reasons, a consent form may be required, but refusing to take the test may have legal consequences.
A test for blood alcohol level is done to:
In general, there's nothing you have to do before this test, unless your doctor tells you to.
A health professional uses a needle to take a blood sample, usually from the arm.
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
In Canada, the federal maximum blood alcohol concentration (BAC) is 0.08 for all fully licensed drivers. Most provinces have legal consequences starting at levels as low as 0.05. Legal limits are set lower for drivers who are not fully licensed.
No alcohol is found in the blood.
Any alcohol is found in the blood.
Having any amount of alcohol in the blood can cause poor judgment and slowed reflexes. BAC and the effects of drinking alcohol vary from person to person and depend upon body weight, the amount of food eaten while drinking, and each person's ability to tolerate alcohol.
Estimated blood alcohol concentration (BAC)
Relaxation, slight body warmth
Sedation, slowed reaction time
Slurred speech, poor coordination, slowed thinking
Trouble walking, double vision, nausea, vomiting
May pass out, tremors, memory loss, cool body temperature
Trouble breathing, coma, possible death
0.50 and greater
Blood alcohol concentration (BAC) is a measurement of how much alcohol you have in your body. This can be used to determine when someone is legally intoxicated (drunk).
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.
Here are some examples of BAC and its effect:
BAC depends on the number of drinks you have and the strength of alcohol (proof or percentage) in the drinks. Other things that affect blood alcohol levels include:
Current as of: March 22, 2023
Author: Healthwise StaffMedical Review: E. Gregory Thompson MD - Internal MedicineAdam Husney MD - Family MedicineMartin J. Gabica MD - Family MedicineKathleen Romito MD - Family MedicineR. Steven Tharratt MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical ToxicologyJoLynn Montgomery PA - Family Medicine
Current as of: March 22, 2023
Author: Healthwise Staff
Medical Review:E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & Martin J. Gabica MD - Family Medicine & Kathleen Romito MD - Family Medicine & R. Steven Tharratt MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology & JoLynn Montgomery PA - Family Medicine
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