CDT Testing Detects Heavy Drinking

Test Can Detect Harmful Alcohol Consumption, Relapse

Vial of Blood
Blood Test Can Detect Heavy Drinking. © Getty Images

Healthcare providers who are concerned that their patients may be drinking alcohol at harmful levels have a blood test they can use to determine if they are indeed drinking too much.

The carbohydrate-deficient transferrin (CDT) test, approved in 2001 by the FDA as an alcohol biomarker test, can be used to detect if someone is a binge drinker or a daily heavy drinker (4 or more drinks a day). It can even be used to determine if an alcoholic has had a relapse.

Medical Reasons Not to Drink

There are many medical situations in which a patient should not consume alcohol, or not consume large amounts of alcohol. People with diabetes or high blood pressure, for example, should not drink heavily, nor should anyone with Hepatitis C or liver disease.

Patients who are taking certain medications should not drink due to the risk of having a reaction between the medication and the alcohol. People who are being treated for pain with opioid painkillers or those who are taking sedatives or sleep aids certainly should not drink alcohol heavily due to the risk of their central nervous system shutting down.

Self-Reporting Tests Unreliable

Traditionally, doctors and other healthcare providers used brief alcohol screening tests to determine if the level of their patients' alcohol consumption. The problem with those screening tests is their results depends on the patient being honest about how much they drink.

Patients who don't have an alcohol problem, probably most accurately self-report their level of consumption, but those who do have a problem are more likely to minimize their drinking levels. The greater the problem, the more likely the patient will deny the heavy alcohol consumption.

Therefore, those brief screening tests administered in a healthcare setting may not produce the most accurate assessment.

The CDT test gives the healthcare provider another tool when they suspect the patient may be abusing alcohol.

What Is the CDT 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 - the carbohydrate-deficient kind.

When carbohydrate-deficient transferrin increases, it can be measured in the bloodstream and therefore is a biomarker of alcohol abuse.

How Does the CDT Test Work?

People who do not drink or drink moderately, will have lower carbohydrate-deficient transferrin levels in their blood, some studies use a cut off of less that 1.7%. But, people who drink 4 or more drinks a day, at least five days a week for two weeks prior to the test will have CDT at significantly greater levels.

For patients who drink a bottle of wine, five beers or half a pint of whiskey a day, the CDT test is highly accurate in detecting that level of heavy drinking.

Much in the same way that an A1C test can detect glucose levels in the blood over a period of 90 days, the CDT test can detect heavy alcohol consumption over a long period of time.

If the person stops drinking, the CDT levels will decrease, but if they start drinking again, the levels will once again increase.

False Positives

First, not everyone is CDT sensitive. In a small percentage of the population, heavy alcohol consumption does not raise the level of carbohydrate-deficient transferrin. Therefore, healthcare providers who suspect heavy drinking in their patients are encouraged to use other alcohol biomarker testing as well.

There are some biological factors that can falsely increase CDT levels, such as genetic variants, female hormones, iron stores, low body mass index, catabolic states, chronic pulmonary disease and end-stage liver disease.

The initial CDT tests would return false positives due to the above factors, but now newer tests can identify genetic variants that can cause false positives and negatives, as well as patterns caused by liver disease related to heavy drinking.

Collecting More Information

There have been many studies conducted on the effectiveness of using the CDT test to determine heavy drinking in patients, and although those studies find that the test is the most accurate, it is not foolproof.

Researchers suggest that if a patient's CDT test indicates harmful drinking, that healthcare providers use other methods to help confirm the results - including the use of questionnaires, a GGT (gamma-glutamyl transpeptidase) test, or a EtG (ethyl glucuronide) test (which detects alcohol consumption in the past 24-72 hours).

Why Is CDT Testing Important?

One of the research studies that used CDT testing among patients with diabetes and hypertension found that of the 799 patients studied, 9% of the diabetics and 15% of those with high blood pressure were drinking at harmful levels.

If those percentages hold nationwide, it could mean that 1.35 million diabetics and 7.5 million hypertension patients are drinking at levels that are putting their health at risk.

Therefore, the researchers suggest that healthcare costs could be reduced significantly if healthcare providers used the CDT test to identify their patients with diabetes, hypertension and other conditions who are drinking too much.

Useful in Monitoring Recovery

In addition to detecting heavy drinking in patients with alcohol-sensitive conditions, CDT testings can be used in the substance abuse field to monitor abstinence and relapse.

Some psychotherapists and psychiatrists who work with alcoholics use the CDT test to get a baseline level when they first have contact with the patient. In the weeks and months that follow, they can use future CDT tests to determine if the person is remaining sober or has secretly had a relapse.

According to researchers, the CDT test is the only alcohol biomarker that is sensitive enough to detect reductions in alcohol use or relapse.


Bianchi, V. et al. "A comparison between serum carbohydrate-deficient transferrin and hair ethyl glucuronide in detecting chronic alcohol consumption in routine." Alcohol and Alcoholism May 2015.

Das, SK. et al. "Should we use carbohydrate deficient transferrin as a marker for alcohol abusers?" Journal of Clinical Biochemistry July 2004

DeGiovanni, N, et al. " The usefulness of biomarkers of alcohol abuse in hair and serum carbohydrate-deficient transferrin: a case report." Drug Testing and Analysis December 2014

Fleming, M. at al. " Carbohydrate-Deficient Transferrin: Validity of a New Alcohol Biomarker in a Sample of Patients with Diabetes and Hypertension." Journal of the American Board of Family Medicine July 2004

Medical University of South Carolina. "Heavy Alcohol Testing - Carbohydrate Deficient Transferrin (%CDT) and Urine Ethylglucuronide (EtG) Testing." Institute of Psychiatry Accessed June 2015

U.S. National Library of Medicine. "Gamma-glutamyl transpeptidase." Medical Encyclopedia Accessed June 2015

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