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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:
No special preparation is needed before having a blood alcohol test.
Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
The health professional drawing blood will:
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
A blood alcohol test measures the amount of alcohol (ethanol) in your body. Some states have no set limit for legal intoxication. But the National Highway Traffic Safety Administration (NHTSA) recommends that all states set the legal definition of intoxication as the point when the blood alcohol concentration (BAC) exceeds 0.08 (which is equivalent to 80 mg/dL or 17 mmol/L).
No alcohol is found in the blood.
Any alcohol is found in the blood.
Legal intoxication is defined as having a blood alcohol concentration (BAC) of 0.08 or greater. But the legal blood alcohol concentration (BAC) limit for people under age 18 may be lower, such as 0.02.
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
Reasons you may not be able to have the test or why the results may not be helpful include:
Things that affect how quickly the blood alcohol level rises in the body include:
Current as ofJune 25, 2018
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, FACP, FCCP - Pulmonology, Critical Care Medicine
Current as of:
June 25, 2018
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, FACP, FCCP - Pulmonology, Critical Care Medicine
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