Alcohol & Health
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Updated on December 10, 2022
4 min read

Can a Blood Test Show Heavy Drinking?

Can You Drink Alcohol Before a Blood Test?

If you are getting blood work done, it's best to avoid alcohol consumption, especially for fasting blood tests. Drinking alcohol can cause irregular enzymes, blood sugar, and fat levels and give inaccurate blood test results.

Avoid drinking alcohol before taking these common blood tests:

  • Cholesterol tests
  • Triglyceride tests
  • Lipid panel blood tests
  • Blood glucose tests
  • Hepatitis tests
  • Liver function tests

If you have a blood test coming up and are unsure whether you can drink or not, it's best to avoid drinking any alcohol at all, especially the night before.

Consult a healthcare professional for more medical advice if you have further questions or want to explore treatment options/resources.


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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 content (BAC).

So if you're wondering if a blood test can show how heavy you've been drinking, then the answer is yes. However, blood alcohol tests are only accurate six to 12 hours after the last drink. 

In general, blood tests are used to help identify the following:

  • Liver disease or damage
  • Excessive alcohol use
  • Changes in alcohol consumption during recovery

Direct and Indirect Biomarkers 

effectiveness of biomarker

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. 


Blood tests are useful tools used in measuring blood alcohol concentration. Between direct and indirect biomarkers, direct biomarkers are considered more accurate, with an accuracy rate of 99 percent.

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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: 

CDT testing measures 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 daily (at least five days a week for two weeks before the test). These people tend to have significantly higher levels of carbohydrate-deficient transferrin.

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Effectiveness of CDT Tests

CDT testing is accurate but not foolproof.

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 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.


Carbohydrate-deficient transferrin (CDT) is an alcohol biomarker test. Although not completely perfect, it is a very sensitive test that can detect a relapse or a decrease in alcohol consumption.

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:

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 intake.


There are many types of biomarkers used to measure blood alcohol concentration. Factors like age, gender, health status, and ethnicity affect different biomarkers. Use a combination of different biomarker tests to get accurate results.

Alcohol Use Statistics



of Americans ages 18 and older reported that they drank alcohol in their lifetime.



of Americans ages 18 and older reported that they engaged in binge drinking in the last month.



people have alcohol use disorder (AUD).

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Updated on December 10, 2022
6 sources cited
Updated on December 10, 2022
All Alcoholrehabhelp content is medically reviewed or fact checked to ensure as much factual accuracy as possible.

We have strict sourcing guidelines and only link to reputable media sites, academic research institutions and, whenever possible, medically peer reviewed studies.
  1. Liang, S., et al. “Evaluation of the diagnostic utility of carbohydrate-deficient transferrin in chronic alcoholism: Results from Southwest China.” Medicine, 2021.
  2. Biomarkers of Heavy Drinking.” National Institute on Alcohol Abuse and Alcoholism, 2019.
  3. How Testing Blood for Alcohol Abuse Works: Options Listed.” Www.Dnalegal.Com, 2016.
  4. Alcohol Use Biomarkers | ARUPConsult Lab Test Selection.” Arupconsult.Com, 2022.
  5. "Alcohol facts and statistics." National Institute on Alcohol Abuse and Alcoholism, 2020.
  6. Andresen-Streichert, H., et al. “Alcohol Biomarkers in Clinical and Forensic Contexts.” Deutsches Arzteblatt international, 2018.

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