There are several tests to 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 of an alcohol blood test. 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. These tests can also show how much alcohol a person has consumed. There are several legal reasons a person might be asked to take one of these tests. This includes:
- to test if they were driving under the influence of alcohol
- to test if they were drinking while being under the legal drinking age
- to test if they were intoxicated at the time of a motor vehicle accident
- as part of the conditions of probation or parole
- as part of a criminal investigation
- during a pre-employment screening
- to test if they were drinking on the job
- to test for alcohol poisoning so that appropriate medical treatment can be given
- as part of 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 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 their 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 multiple drinks regularly.
- Phosphatidylethanol (PEth): PEth levels in the body are affected by alcohol use for up to 2 weeks.
- Ethyl glucuronide/Ethyl sulfate (EtG/EtS): These chemicals are
typically measuredin 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. However, 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.
- Sober: 0.0% BAC
- Legally intoxicated: 0.08% BAC
- Very impaired: 0.08% to 0.40% BAC
- At risk for complications (including coma or death): above 0.40% BAC
It’s important to remember levels of intoxication feel different for different people. For instance, someone could have .03% BAC and still be very intoxicated and unable to drive.
Additionally, laws vary by state. Although the legal limit for driving is .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 of the primary differences is that blood tests are a lot more reliable and accurate. Breathalyzers can produce false positives because the test relies on a person blowing into the resting device. This can bring in alcohol that was in the person’s mouth, not their blood, and can cause false positives and reads that are too high.
- recent mouthwash use
- recent consumption of food that was cooked in alcohol
- not having eaten in a while
- certain medications
- recent or frequent inhaler use
- denture wear
- a recent burp
- cough syrup
Still have questions? You can learn more about alcohol blood tests by reading the answers to some common questions below.
How long does alcohol stay in the bloodstream?
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.
Can a blood test show heavy drinking?
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 a 2- to 3-week window.
What can cause a false positive on an alcohol blood test?
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.
How long does an alcohol blood test take to get results?
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.
Will drinking alcohol the night before affect blood work?
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 A1C test.
What blood test shows liver damage from alcohol?
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 caused by alcohol.
Changing your relationship with alcohol can feel overwhelming, but there are resources that can help. When you’re ready, you can check out:
- The Substance Abuse and Mental Health Services Administration (SAMHSA) Helpline: You can call 1-800-662-4357 to get information and referrals to local resources. The service is available 24 hours a day, 7 days a week. The helpline is completely free, and representatives speak both English and Spanish.
- The National Institute on Alcohol Abuse and Alcoholism (NIAAA): The NIAAA provides a free
treatment navigatorthat can help you find recovery programs, therapists, and medical care in your local area.
- Alcoholics Anonymous (AA): AA takes a 12-step recovery approach and has chapters all over the United States and online.
- SMART Recovery: SMART Recovery is a recovery platform and program that offers resources, tools, and supportive community spaces to help you succeed.
- Women for Sobriety: Women for Sobriety offers a wealth of resources, including in-person meetings, online support, and phone counseling. Women for Sobriety welcomes all women looking to quit alcohol or drugs.
- Gays and Lesbians in Alcoholics Anonymous (GaL-AA): GaL-AA can help members of the LGBTQ community find welcoming and supportive AA meetings.
Alcohol blood tests are used to measure blood content. This test can tell if someone has been drinking recently, and it can tell 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 are 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.