Can a Blood Test Show Heavy Drinking?

Blood Tests and Heavy Alcohol Consumption

Blood tests are one of the most reliable methods for detecting heavy alcohol consumption. They can also effectively measure blood alcohol level (BAC). While effective, there are a few things to know about the tests before accepting the test results.

Approximately one-fifth of primary care patients in the United States drink alcohol to the point where it harms their health. Research also shows that people who drink unhealthy amounts of alcohol tend to underestimate how much they consume. This makes blood testing a useful tool for measuring realistic alcohol consumption, especially for those seeking treatment. 

Testing is also used in health care for people managing conditions related to alcohol consumption, such as liver disease or liver damage.


Direct and Indirect Biomarkers 

Most blood tests rely on direct and indirect biomarkers, which show how a person’s organs function. 

Indirect biomarkers are affected by alcohol consumption, but alcohol is not the only thing that can affect them. 

Direct biomarkers, on the other hand, only arise after alcohol consumption. This makes them an accurate predictor of the amount of alcohol someone has recently consumed. 

In the past, blood tests relied on indirect markers to determine BAC. In some cases, indirect biomarker tests are as low as 44 percent accurate. Direct biomarker testing is approximately 99 percent accurate. The results from a direct biomarker blood test are even more reliable when confirmed through fingernail and hair testing results. 


CDT Testing for Alcohol Abuse

CDT Testing, which is short for carbohydrate-deficient transferrin, is an alcohol biomarker test. Transferrin is a substance in the blood that carries iron to the bone marrow, liver, and spleen. When someone drinks too much, it increases certain types of transferrin that are carbohydrate-deficient. It also helps determine if someone is: 

  • Misreporting alcohol consumption
  • Drinking heavily
  • Binge drinking
  • Struggling with alcohol relapse

CDT testing works by measuring the amount of carbohydrate-deficient transferrin in a person’s system. Moderate drinkers or non-drinkers have lower levels of carbohydrate-deficient transferrin. 

Heavy drinkers drink four or more drinks per day (at least five days a week for two weeks before the test). These people tend to have significantly higher levels of carbohydrate-deficient transferrin.

Effectiveness of CDT Tests

CDT testing is accurate, but not full-proof. This is because heavy drinking doesn’t trigger an increase in carbohydrate-deficient transferrin for everyone. If someone suspected of drinking has low carbohydrate-deficient transferrin, medical professionals encourage follow-up use of other alcohol biomarker tests for the most accurate results.

Despite it being imperfect, CDT testing is the only test sensitive enough to detect relapse or reduction in alcohol use. Many therapists use CDT testing to determine a baseline level for patients when treatment begins.


Alcohol Use Biomarkers

Other biomarker tests support or disprove the results of a CDT test. Selecting the proper test varies from person to person. 

The best tests are easy to obtain, inexpensive to evaluate, and acceptable to patients and therapists. 

Biomarkers differ based on several factors, including:

  • Age
  • Gender
  • Ethnicity
  • Health status

The specific markers used to detect a high level of alcohol exposure include:

  • Ethanol
  • Ethyl sulfate (EtS)
  • Ethyl glucuronide (EtG)

Specific markers for chronic alcohol use include:

  • Carbohydrate-deficient transferrin (CDT)
  • Phosphatidylethanol (PEth)

Nonspecific markers include: 

  • Aspartate aminotransferase (AST)
  • Alanine aminotransferase (ALT)
  • Gamma-glutamyl transferase (GGT)
  • Mean corpuscular volume (MCV)

Each biomarker testing method has advantages and disadvantages. Experts recommend using a combination of tests to confirm the status of a person’s alcohol consumption.

Resources “How a CDT Test Detects Dangerous Alcohol Consumption.” Verywell Mind, 2019,

“Biomarkers of Heavy Drinking.” Nih.Gov, 2019,

“How Testing Blood for Alcohol Abuse Works: Options Listed.” Www.Dnalegal.Com,

“Alcohol Use Biomarkers | ARUPConsult Lab Test Selection.” Arupconsult.Com, 2019,

Updated on: August 13, 2020
Alcohol Rehab Help Writing Staff
Medically Reviewed
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Annamarie Coy,
All content created by Alcohol Rehab Help is sourced from current scientific research and fact-checked by an addiction counseling expert. However, the information provided by Alcohol Rehab Help is not a substitute for professional treatment advice. For more information read out about us.

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