Several tests measure the level of alcohol in your blood. These procedures are typically simple but may take several weeks to get results.

A blood alcohol test measures the percentage of alcohol in a sample of your blood. This test can measure your level of intoxication. It’s often used for legal reasons, such as testing if someone was driving while under the influence of alcohol.

An alcohol blood test is performed in a medical facility. The blood sample will be sent to a lab for analysis, and results won’t be available right away. In some cases, it can take weeks to receive the results.

However, alcohol blood tests are more accurate than alternatives, such as breathalyzers, and are much less likely to produce false positives.

An alcohol blood test can verify if a person has recently consumed alcohol (in the past 12 hours). These tests can also show how much alcohol a person has consumed.

Blood alcohol tests have many uses, including:

  • determining if someone was driving under the influence of alcohol
  • checking for underage drinking
  • assessing intoxication of a person at the time of a motor vehicle accident
  • meeting the conditions of a person’s probation or parole
  • assisting in criminal investigations
  • checking for alcohol use as part of pre-employment screenings
  • verifying if someone was drinking while performing their job
  • diagnosing alcohol poisoning to help determine appropriate medical treatment
  • supporting a person involved in an alcohol treatment program

A blood alcohol test is done at a lab. If you need to take one, you’ll be asked to go to a medical facility to have your blood drawn. This process is longer than the breathalyzer alcohol test that many people associate with alcohol testing in situations like driving under the influence. However, blood tests are known to be more accurate.

There are a few different types of blood alcohol tests. The most common type is used to show the amount of alcohol a person has consumed recently. This is called blood alcohol content (BAC). There are also tests that are used to measure chronic alcohol use and the buildup of alcohol biomarkers in the body. This includes:

  • carbohydrate-deficient transferrin (CDT): CDT is a test that can identify heavy alcohol use. Increased levels of CDT show that a person has been consuming alcoholic drinks regularly.
  • phosphatidylethanol (PEth): PEth levels in the body are affected by alcohol use for 3 to 4 weeks.
  • ethyl glucuronide/ethyl sulfate (EtG/EtS): These chemicals are typically measured in urine after drinking, but they can also be measured in the blood.

A BAC test is the most common type of blood alcohol test. It’s the one used for most legal, medical, and employment testing.

CDT tests are often used for people who are part of alcohol treatment programs or who have health conditions associated with alcohol dependence. PEth results are typically used in research, not diagnostic testing.

The results of a blood alcohol test will show the percentage of blood alcohol content. The results of a blood alcohol test are only for 6 to 12 hours following a person’s last drink. Possible results of a blood alcohol test are:

  • Sober: 0.0% BAC
  • Legally intoxicated: 0.08% BAC
  • Very impaired: 0.08% to 0.40% BAC
  • At risk of complications (including coma or death): above 0.40% BAC

It’s important to remember that levels of intoxication can feel different for different people. For instance, someone could have 0.03% BAC yet still be very intoxicated and unable to drive.

Additionally, laws vary by state. Although the legal limit for driving is 0.08% in all states, penalties vary sharply. Plus, in some states, drivers under the age of 21 have a different, much lower, legal BAC percentage threshold.

Alcohol blood test vs. breathalyzer

Alcohol blood tests and breathalyzers are both used to measure intoxication, but there are key differences.

One primary difference is that blood tests are much more reliable and accurate.

Breathalyzers can produce false positives because they rely on a person blowing into the testing device. This can bring in alcohol that was in the person’s mouth, not their blood, and can cause false positives and readings that are too high.

For instance, false positives on breathalyzers might be the result of:

  • alcohol left in the mouth from a recent drink
  • alcohol from the stomach coming back into the mouth from regurgitation, burping, vomiting, or hiccuping
  • alcohol from other sources, such as hand sanitizers, E85 gasoline, inhalers, mouthwash, tobacco, food, drinks, and dental appliances

Still have questions? Learn more about alcohol blood tests by reading the answers to some common questions below.

Alcohol typically stays in the bloodstream between 6 and 12 hours.

Factors, such as your metabolism, body weight, genetics, age, overall health, medications taken, and the amount of food eaten that day, can all play a role in how long it takes alcohol to leave your bloodstream.

Blood tests can show heavy drinking, but only within certain time frames. A BAC test can show drinking within a 6- to 12-hour window. A CDT test can show heavy drinking in the past 3 weeks.

Alcohol blood tests are much less susceptible to false positives than breath tests, such as breathalyzers. However, it’s still possible for false positives to occur.

The most common reasons are blood samples that aren’t handled correctly or that become contaminated during testing.

The results of a breathalyzer are instant, but the results of an alcohol blood test can take weeks. The time it takes for you to get the results will likely depend on the reason the test was required.

For instance, pre-employment testing often has a fast turnaround window to help speed up the hiring process, so you might know those results within a few days. However, if the test was related to suspected driving under the influence, results often take several weeks.

If you’re having any kind of blood work, it’s typically a good idea to avoid alcohol the night before. Alcohol can affect your blood sugar and fat levels. This can give inaccurate results to common lab work, such as a lipid panel or an A1C test.

Liver function tests are blood tests that are used to see how well your liver is performing. Liver function tests include a gamma-glutamyl transpeptidase (GGT) test. GGT is an enzyme that’s produced in your liver. The level of GGT in your blood indicates liver damage, often caused by alcohol.

It can show excessive alcohol intake between 2 and 6 weeks after consumption.

Alcohol blood tests can tell if someone has been drinking recently and how much that person has been drinking.

Often, these tests are used for legal matters, such as suspicion of driving under the influence or underage drinking. But they’re also common for pre-employment testing, as part of alcohol rehabilitation programs, and to test for alcohol poisoning.

Blood alcohol tests are more reliable than breathalyzers and less likely to produce false positives. Results can take a few weeks, but will be based on alcohol consumed in the 6 to 12 hours before the test.

If you are concerned about your alcohol use, know that you’re not alone and there are many options that may help you. Speaking with a therapist can help you understand your reasons for drinking alcohol and help you find tools to reduce or stop your intake.