Home > Health Library > Blood Alcohol
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.
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
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
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
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
No alcohol is found in the
Any alcohol is found in the
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
Relaxation, slight body warmth
Sedation, slowed reaction time
Slurred speech, poor coordination, slowed
Trouble walking, double vision, nausea,
May pass out, tremors, memory loss, cool
Trouble breathing, coma, possible
Reasons you may not be able to
have the test or why the results may not be helpful include:
Many medicines may change the results of this test. Be sure
to tell your doctor about all the nonprescription and prescription medicines
Things that affect how quickly the blood
alcohol level rises in the body include:
Other Works Consulted
Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise StaffPrimary Medical ReviewerE. Gregory Thompson, MD - Internal MedicineSpecialist Medical ReviewerR. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
Current as ofAugust 21, 2015
Current as of:
August 21, 2015
E. Gregory Thompson, MD - Internal Medicine & R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care Medicine, Medical Toxicology
To learn more about Healthwise, visit Healthwise.org.
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