Addiction Alcohol Use How CDT Testing Detects Harmful Alcohol Consumption By Buddy T Buddy T Facebook Twitter Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism. Learn about our editorial process Updated on March 19, 2022 Medically reviewed Verywell Mind articles are reviewed by board-certified physicians and mental healthcare professionals. Medical Reviewers confirm the content is thorough and accurate, reflecting the latest evidence-based research. Content is reviewed before publication and upon substantial updates. Learn more. by Steven Gans, MD Medically reviewed by Steven Gans, MD Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital. Learn about our Medical Review Board Print Frances Twitty / Getty Images Table of Contents View All Table of Contents What Is a CDT Test? How It Works When and Why CDT Is Tested Accuracy When gauging alcohol use in their patients, healthcare providers rely mainly on three methods: Traditional brief screeningThe blood alcohol concentration (BAC) testThe carbohydrate-deficient transferrin (CDT) test The traditional brief alcohol screening isn't as reliable as the other two methods because its accuracy depends solely on the patient being accurate and honest about how much they drink. While the BAC test measures the level of alcohol currently in the bloodstream, CDT testing uses biomarkers to detect a recent history of harmful levels of alcohol consumption. The CDT test is a better indicator of binge drinking or daily heavy drinking (four or more drinks per day) than the other two tests. It can even help determine if a person with alcohol use disorder has had a relapse. What Constitutes Heavy Drinking? The Centers for Disease Control and Prevention (CDC) defines heavy drinking as consuming at least 15 drinks/week (for men) or eight drinks/week (for women). Notably, an estimated 90% of heavy drinkers don't meet the diagnostic criteria for moderate or severe alcohol use disorder, a chronic brain disease that interferes with daily life. Can Alcohol Screening Tests Detect Drinking Problems? What Is a CDT Blood Test? As the name suggests, CDT blood testing measures the level of CDT in the bloodstream. Carbohydrate-deficient transferrin (CDT) is a substance that carries iron to the bone marrow, liver, and spleen. When someone drinks heavily, the level of CDT in their body increases to a point at which it can be measured in a blood sample. Therefore, this increase is a biomarker of excessive alcohol use. What Is a Biomarker? A biomarker (short for "biological marker") is a molecule in the body that signals some condition or process. Healthcare providers and researchers use biomarkers in diagnosis, treatment, and testing—for example, to check how well a cancer treatment is working or to detect high cholesterol. How Long Does Alcohol Stay in Your System? How the CDT Test Works People who do not drink, or drink only moderately, have lower CDT levels in their blood than those who drink heavily. Some CDT tests use a cutoff of less than 1.7%. People who drink four or more drinks a day, at least five days a week, for two weeks prior to the test show significantly greater levels of CDT. The CDT test is highly accurate in detecting heavy drinking. Similar to how an A1C test detects blood glucose levels over the previous 90 days, the CDT test detects heavy alcohol consumption over a long period. When a person stops drinking, CDT levels go back to normal after two to four weeks. Likewise, if they resume drinking, the levels once again increase after a few days. How Much Alcohol Is Safe to Drink? When and Why CDT Is Tested The CDT test gives a healthcare provider a far more reliable diagnostic tool than the traditional brief alcohol screening test, which relies on a patient's honesty about their drinking habits. Patients who don't consume alcohol excessively tend to self-report accurately, but those who do are more likely to minimize their drinking levels. The greater the misuse, the more likely the person will deny heavy alcohol consumption. Medical Conditions Alcohol consumption is contraindicated for many medical conditions. People with diabetes, high blood pressure, hepatitis C, or liver disease should not drink heavily. One study found that of 799 patients studied, 9% of subjects with diabetes and 15% of those with high blood pressure were consuming alcohol at harmful levels. When extrapolated to the population at large, these results could mean that millions of people with diabetes and hypertension are risking their health by drinking alcohol. Using the CDT test to identify patients with diabetes, hypertension, and other conditions who are drinking too much could reduce medical complications and healthcare costs significantly. Drug Interactions Patients who take certain prescription and over-the-counter medications can experience harmful effects if they drink alcohol. Similarly, people who are being treated with opioid painkillers, sedatives, or sleep aids risk central nervous system depression should they drink alcohol heavily. In a medical emergency, CDT testing could uncover alcohol use that's reacting with medications and causing problems. Recovery CDT testing also can help healthcare providers monitor abstinence and relapse because the test is sensitive enough to detect increases and decreases in alcohol use. Some psychotherapists and psychiatrists use the CDT test to determine a baseline level when they first begin treating a patient for alcohol use disorder. In the weeks and months that follow, they can use the CDT test to determine if the person is remaining sober or has had a relapse. Warning Signs of a Drug or Alcohol Relapse Accuracy of CDT Tests Researchers have conducted many studies on the effectiveness of using CDT testing to identify heavy alcohol consumption. Those studies find that the test is accurate but not foolproof. Confirmation methods include the use of a questionnaire, a gamma-glutamyl transpeptidase (GGT) test, or an ethyl glucuronide (EtG) test (which detects alcohol consumption in the previous 24 to 72 hours). False Negatives In a small percentage of people, heavy alcohol consumption does not raise levels of CDT in the blood. A healthcare provider who suspects heavy drinking despite a negative CDT test may then turn to digital DNA methylation techniques, which rely on blood or saliva samples to detect heavy alcohol consumption. False Positives Biological factors such as genetic variants, female hormones, and end-stage liver disease can falsely increase CDT levels. The earliest CDT tests returned false positives due to these factors, but 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. How Daily Drinking Increases Risk of Serious Liver Disease 9 Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Solomons HD. Carbohydrate deficient transferrin and alcoholism. Germs. 2012;2(2):75-78. doi:10.11599/germs.2012.1015 Liang SS, He Y, Huang ZG, Jia CY, Gan W. Evaluation of the diagnostic utility of carbohydrate-deficient transferrin in chronic alcoholism. Medicine (Baltimore). 2021;100(4):e24467. doi:10.1097/MD.0000000000024467 Alcohol questions and answers. CDC. Dictionary of cancer terms. National Cancer Institute. Fagan KJ, Irvine KM, McWhinney BC, et al. Diagnostic sensitivity of carbohydrate deficient transferrin in heavy drinkers. BMC Gastroenterol. 2014;14:97. doi:10.1186/1471-230X-14-97 Carbohydrate-Deficient Transferrin (CDT), Adult. Labcorp. Harmful interactions. National Institute on Alcohol Abuse and Alcoholism(NIAAA). Conigrave KM, Degenhardt LJ, Whitfield JB, et al. CDT, GGT, and AST as markers of alcohol use: The WHO/ISBRA collaborative project. Alcohol Clin Exp Res. 2002;26(3):332-9. Miller S, A Mills J, Long J, Philibert R. A comparison of the predictive power of DNA methylation with carbohydrate deficient transferrin for heavy alcohol consumption. Epigenetics. 2021;16(9):969-979. doi:10.1080/15592294.2020.1834918 Additional Reading Bianchi V, Premaschi S, Raspagni A, Secco S, Vidali M. A comparison between serum carbohydrate-deficient transferrin and hair ethyl glucuronide in detecting chronic alcohol consumption in routine. Alcohol Alcohol. 2015;50(3):266-70. doi:10.1093/alcalc/agv005 De Giovanni N, Cittadini F, Martello S. The usefulness of biomarkers of alcohol abuse in hair and serum carbohydrate-deficient transferrin: a case report. Drug Test Anal. 2015;7(8):703-7. doi:10.1002/dta.1763 U.S. National Library of Medicine. Gamma-glutamyl transpeptidase. Updated January 26, 2019. By Buddy T Buddy T is an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism. See Our Editorial Process Meet Our Review Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit Get Treatment for Addiction Advertiser Disclosure × The offers that appear in this table are from partnerships from which Verywell Mind receives compensation.