About the Test
Purpose of the test
Alcohol blood testing may be used to determine if a person has recently consumed alcohol and/or to understand the pattern of a person’s alcohol use. Alcohol in the blood may be measured for a variety of purposes:
- Workplace testing: Employers may test for alcohol use in new applicants, regularly during employment, or after an accident on the job. Although most private employers are not required to test employees for the use of alcohol and other drugs, testing is required in certain safety- and security-sensitive workplaces, such as the Department of Defense and the Department of Transportation.
- Legal testing: Alcohol blood testing may be used during an investigation or court case. This test can be used to identify under-age drinking, monitor for alcohol use while a person is on parole, and to determine if a person is driving while impared.
- Medical testing: Alcohol blood testing is an important test for diagnosing alcohol poisoning, a potentially life-threatening result of consuming large amounts of alcohol.
- Monitoring alcohol use disorder: Testing for alcohol use is part of some approaches to the treatment of alcohol use disorder, also called alcohol abuse or alcoholism. Testing can help health professionals understand if a person is continuing to drink alcohol while in recovery.
What does the test measure?
An alcohol blood test measures the amount of alcohol, biomarkers, or metabolites in a person’s blood or serum. Serum is the liquid part of blood that remains after blood clots. Alcohol metabolites are substances that are created as the liver breaks down and the body rids itself of alcohol, while an alcohol biomarker is a substance that is only present following alcohol consumption.
A common way to measure alcohol use is to determine the amount of alcohol in a person’s blood. The amount of alcohol in a person’s blood is called their blood alcohol content (BAC) or blood alcohol concentration.
Once consumed, alcohol stays in a person’s body until it is broken down, primarily by the liver. When a person drinks faster than their liver can break down alcohol, their BAC increases.
While measuring a person’s BAC can show the amount of alcohol they’ve consumed recently, alcohol metabolites can be measured to measure chronic alcohol use or relapse after a period of sobriety. Several alcohol biomarkers can be measured in the blood, including:
- Carbohydrate-deficient transferrin (CDT): CDT helps doctors identify heavy alcohol use. Increased levels of CDT suggest that a person may be consuming more than 50 to 80 grams of alcohol, roughly equivalent to 3 to 6 drinks, per day for two to three weeks.
- Phosphatidylethanol (PEth): Levels of PEth are closely aligned with the amount of alcohol a person consumes. This test is mostly used in research studies at this time.
Additionally, ethyl glucuronide and ethyl sulfate (EtG/EtS) are alcohol metabolites that are typically measured in urine and sometimes in blood. Although EtG/EtS can detect evidence of alcohol much longer than ethanol testing, testing for EtG/EtS does not indicate the amount or frequency of alcohol consumption. The results of this test may be positive after even a small amount of alcohol is ingested.
Alcohol use can be detected in the blood within minutes of a person’s first drink. The timeframe in which alcohol use can be detected in the blood, called its detection window, depends on several factors, including the type of test conducted. The following table shows the estimated detection windows for alcohol blood tests:
| Alcohol Detection Windows After Last Drink | |
|---|---|
| Test | Estimated Detection Window in the Blood |
| Blood Alcohol Content | 6 to 12 hours |
| Carbohydrate-Deficient Transferrin (CDT) | 2 to 3 weeks |
| Phosphatidylethanol (PEth) | 1 to 2 weeks or longer |
| Ethyl Glucuronide/Ethyl Sulfate (EtG/EtS) | Up to 80 hours |
When should I get an alcohol blood test?
An alcohol blood test may be ordered in a variety of situations in which it’s important to detect recent alcohol use or measure the level of alcohol in the body. When a person can be tested for alcohol and other drugs is impacted by federal, state and local laws.
Federal employees may be required to undergo regular drug testing as part of a drug-free workplace program. Drug-free workplace programs are required by federal law in certain industries, including transportation and national security.
Law enforcement officers and emergency service providers may also be required to undergo drug testing.
Finding an Alcohol Blood Test
How to get tested
Alcohol blood testing is performed in a medical facility or laboratory. A test may be ordered by a health care provider or the administrator of a program that is requiring testing.
Can I take the test at home?
At-home alcohol blood testing is not currently available. Patients who are interested in at-home tests that measure alcohol in the body may find it helpful to talk to their doctor about at-home alcohol urine testing and personal breathalyzers:
- At-home alcohol urine testing: At-home tests are available that detect evidence of alcohol in the urine. However, measuring alcohol in the urine is imprecise and does not always correlate with a person’s blood alcohol content.
- At-home breathalyzers: Breathalyzers are handheld devices that provide estimates of a person’s blood alcohol level using a sample of breath. While breathalyzers are less accurate than alcohol blood tests at measuring a person’s BAC, they are less intrusive than blood and urine tests and provide quick results.
How much does the test cost?
The cost of an alcohol blood test depends on the type of test, where the test is taken, and a patient’s health insurance coverage. Costs may include the office visit, a fee for the blood draw, and the actual laboratory analysis.
Workplace alcohol and drug testing is typically paid for by the employer. If a patient’s doctor orders an alcohol blood test, the costs of testing may be covered by the patient’s health insurance. Depending on the health insurance plan, patients may still be responsible for copays or deductibles.
A patient’s doctor, insurance provider, and the laboratory conducting the test can provide more specific information about the cost of alcohol blood testing.
Taking an Alcohol Blood Test
An alcohol blood test requires a blood sample. The blood sample is drawn from a patient’s vein with a needle before being sent to a lab for testing.
Before the test
No special preparations are necessary for an alcohol blood test.
Patients should tell their doctor about any medicines or substances they’ve consumed that contain alcohol, such as mouthwash, cooking extracts, and certain cold medicines. Consuming any substances that contain alcohol can lead to a positive test result.
During the test
A blood sample is taken by a healthcare professional using a small needle. Before the blood sample is collected, the health care professional may tie an elastic band around the patient’s upper arm to increase blood in the patient’s veins. Once a vein is located, the site is cleaned with an antiseptic. After the needle is inserted into the vein, blood is collected in a test tube.
Patients may experience a small sting when the needle is inserted and removed. Collecting a blood sample usually takes less than five minutes.
After the test
After blood is collected, the health care provider will place pressure on the puncture site with a cotton swab or bandage. Patients may be instructed to keep this in place for a short period to prevent any additional bleeding.
Blood draws are a routine procedure and patients can return to normal activities immediately after the sample is collected.
Alcohol Blood Test Results
Receiving test results
Test results from an alcohol blood test may be available soon after the test is conducted. Patients may receive their results within a few hours to several business days.
Test results can be provided through the testing location, the patient’s doctor, or the organization or agency requiring testing. Test reports may also be available through a patient’s electronic medical record.
Interpreting test results
The results of an alcohol blood test can be reported in several ways, depending on the type of alcohol blood test performed.
For testing that determines a person’s BAC, the amount of alcohol in the blood is reported as a number or a percentage. When reported as a number, a person’s test report indicates the milligrams of ethanol per deciliter of blood (mg/dL) or the millimoles of ethanol per liter of blood (mmol/L). When given as a percentage, the concentration of alcohol in the blood is reported as the percentage of a person’s blood that is alcohol.
A positive BAC test result indicates that alcohol was detected while a negative BAC test indicates that alcohol was not detected during the test. Negative results can indicate that a person hasn’t consumed alcohol within the detection window or that the level of alcohol in the blood did not meet the laboratory’s cutoff value for a positive result. A negative test result does not indicate that a person has never used alcohol.
In most of the United States, a blood alcohol concentration of 0.08% is the legal limit for operating a motor vehicle for drivers aged 21 years or older.
The effects of alcohol on an individual depends on many factors, including how much and how often alcohol is consumed, as well as a person’s age, health, and family history. Due to increased tolerance to the effects of alcohol, chronic users may function normally with high levels of alcohol in the blood. The table below shows some of the physical effects as the concentration of alcohol in the blood increases:
| Effects of Blood Alcohol Concentration | |
|---|---|
| Blood Alcohol Concentration | Examples of Physical Effects |
| 0.02% (20 mg/dL) |
|
| 0.05% (50 mg/dL) |
|
| 0.08% (80 mg/dL) |
|
| 0.10% (100 mg/dL) |
|
| 0.15% (150 mg/dL) |
|
| 0.15% to 0.30% (150 to 300 mg/dL) |
|
| 0.30% to 0.40% (300 to 400 mg/dL) |
|
| Over 0.40% (400 mg/dL) |
|
Are test results accurate?
While no test is accurate 100% of the time, alcohol blood tests are the most accurate method to determine the amount of alcohol in a person’s body. For questions about a patient’s test results, it can be helpful to talk to the patient’s doctor or the test administrator about the laboratory that conducted the test and the accuracy of alcohol blood testing.
Do I need follow-up tests?
Follow up testing may be recommended after an alcohol blood test, depending on the reason for testing and the test result. When patients are being evaluated for alcohol poisoning or ingestion of another form of alcohol, follow up tests may include glucose testing as well as testing of electrolytes and anion gap.
A health care provider may evaluate a patient for alcohol use disorder. Alcohol use disorder is a medical condition in which a person is unable to control or stop alcohol use despite negative social, occupational, or health consequences.
An evaluation for alcohol use disorder involves a series of questions to evaluate a person’s drinking habits, symptoms, and the consequences of their alcohol use. If a patient is determined to meet the criteria for alcohol use disorder, many treatments are available.
Questions for your doctor about test results
Patients receiving testing for alcohol and drug use may find it helpful to talk to their doctor about the way that results are interpreted. Questions that may be helpful include:
- Why am I being tested for alcohol use?
- What is my test result?
- Who will have access to my test result or medical record?
- Will I be retested for alcohol use in the future?
- Are any follow-up tests necessary?
