When gauging alcohol use in their patients, healthcare providers rely mainly on three methods:
- Traditional brief screening
- The blood alcohol concentration (BAC) test
- The 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 Per Day?
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 willdeny 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
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
(Video) Alcohol Testing – Drug Testing for EtG and EtS – Cordant Health SolutionsDictionary 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
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 Tis an anonymous writer and founding member of the Online Al-Anon Outreach Committee with decades of experience writing about alcoholism.
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FAQs
How does a CDT blood test work? ›
The Carbohydrate Deficient Transferrin (CDT) test is a sensitive biomarker that tracks heavy alcohol consumption over an extended period of time. Transferrin carries iron in the blood to the bone marrow, liver and spleen. Drinking too much alcohol increases certain types of transferrin that are carbohydrate-deficient.
Can CDT test detect binge drinking? ›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. 2 It can even help determine if a person with alcohol use disorder has had a relapse.
What is a good CDT test result? ›A CDT level of 1.6% or less suggests no recent alcohol intake. This means that a CDT level up to and including 1.6% would be acceptable as evidence of there being no recent alcohol intake in someone classed as alcohol dependent. A CDT level between 1.7% and 2.2% or more suggests recent excess alcohol intake.
How far back can a CDT test detect alcohol? ›Transferrin remains in the circulation for 7 to 14 days and CDT, therefore, can give an indication of alcohol consumption over this period of time, which gives it an advantage over blood or urine alcohol measurements which only remain elevated for 24-48 hours after alcohol consumption.
What can cause a false positive CDT? ›Primary biliary cirrhosis (PBC) is one of the few nonalcohol-induced liver pathologies that causes false positives in assays of carbohydrate-deficient transferrin (CDT) for diagnosing alcohol abuse.
How do I pass a DVLA CDT test? ›To pass the DVLA medical you need to show the doctor that there isn't any evidence of persistent alcohol misuse in the last six months. You must also show that there isn't any alcohol dependency in the last 12 months.
What is considered a high CDT level? ›Under normal conditions, only about 1 to 2% of transferrin is carbohydrate-deficient. As a result of heavy drinking, it can go as high as 10%. Studies have found that a %CDT of 2.6% and higher is indicative of heavy drinking. About 50 to 70% of heavy drinkers will have a %CDT greater than 2.6%.
Can a blood test show heavy drinking? ›The short answer is yes: blood testing can show heavy alcohol use. However, timing plays a significant role in the accuracy of blood alcohol testing. In a typical situation, blood alcohol tests are only accurate six to 12 hours after someone consumes their last beverage.
What is the CDT level of a non drinker? ›The relationship between CDT values and daily alcohol intake is shown in Figure 1. Among nondrinkers, CDT values ranged from 0.2% to 1.6%. For drinkers, the lowest CDT value was 0.5% (with a daily alcohol intake of 5 g) and the highest was 6.3% (with a daily alcohol consumption of 240 g).
How long does it take for CDT levels to rise? ›Usually, consumption of 50–60 g of alcohol per day chronically (for at least 2 or 3 weeks) increases CDT. The half-life of CDT is usually 14–17 days; values return to normal 3 or 4 weeks after abstinence.
Does smoking raise CDT levels? ›
The link between serum CDT levels and factors such as age, sex, body mass index, ethnicity, and smoking was noted as small and considered clinically insignificant [20].
How long should I not drink alcohol before a DVLA medical? ›DVLA Medical Examination Results
If the refusal was due to alcohol misuse then a minimum period of six months controlled drinking or abstinence must be attained alongside normalisation of blood parameters.
The normal value of the serum CDT concentration is under 60 mg/liter; a value between 60 and 100 mg/liter indicates probable alcoholism, and a value > 100 mg/liter indicates a very high probability of alcoholism (specificity: 99%). Its sensitivity ranges from 60 to 91%, and its specificity ranges from 92 to 100%.
Does taking iron lower CDT levels? ›In nonabusers, iron supplementation therapy significantly decreased CDT levels in patients with iron deficiency anemia (33.7 +/- 6.6 U/L vs. 21.7 +/- 5.2 U/L; P =. 0007), while iron-depletion treatment significantly increased CDT levels in patients with GH (9.7 +/- 2.0 U/L vs.
How does a PEth test work? ›What is PEth Testing? A PEth blood test measures the level of phosphatidylethanol, a direct alcohol biomarker which is found in human blood following alcohol consumption. Phosphatidylethanols are abnormal phospholipids formed in the presence of ethanol (more commonly known as alcohol).
How many drinks raise CDT? ›It has been established that %dCDT can increase after about 2 to 3 weeks of steady alcohol consumption of about 4 to 6 drinks a day (this is equivalent to a bottle of wine, 5 cans of beer, or ½ pint (8 oz.)
Do drugs affect CDT levels? ›Although drugs could theoretically affect CDT, few studies have investigated the role of pharmacological therapy on CDT levels (7); in particular, while enzyme-inducing antiepileptic drugs were reported to increase CDT, angiotensin II receptor antagonists (sartans) have been shown to lower CDT values (3, 8) .
What liver tests show alcohol damage? ›Gamma-glutamyl transpeptidase test.
This is an enzyme that is made in the liver, pancreas, and biliary tract. This test is often performed to assess liver function, to provide information about liver diseases, and to detect alcohol ingestion.
Assessments look for: GGT (Gamma GT) - Gamma-glutamyl transferase is an enzyme from the liver. High levels can indicate alcohol abuse. MCV (Mean Cell Volume) - mean corpuscular volume (size) of the red blood cells.
How long does it take to get DVLA medical results back? ›How long does it take to get DVLA medical results? Following a DVLA medical, it usually takes around 15 days before you can expect to receive the results. This could extend to 90 days if you are asked to provide further information. It also takes a further week for blood test samples to be analysed.
What does a drink driving medical consist of? ›
The medical will consist of giving a sample of blood, maybe a urine sample and undergoing a brief physical examination that may include an eye test. The DVLA appointed doctor will then ask a series of questions for a medical interview, within which the high risk offender will be assessed by the answers they give.
How long does it take for CDT levels to drop? ›The CDT test can thus detect heavy alcohol consumption over a long period of time and is a measure of chronic alcohol consumption. If a person stops drinking, the CDT levels will return to normal levels within 4 weeks.
How long before DVLA medical Should I stop drinking? ›DVLA Medical Examination Results
If the refusal was due to alcohol misuse then a minimum period of six months controlled drinking or abstinence must be attained alongside normalisation of blood parameters.
This test is not intended to detect occasional or light alcohol consumption. An ETG Alcohol test may be more effective at detecting alcohol use in the past 1-3 days. Turnaround for this test CDT blood test is typically 3-6 business days.
Does smoking affect CDT test? ›Our results show that mean CDT increases with increasing reported alcohol consumption even within the range of alcohol use considered to be nonhazardous. We found significant effects of sex, age, smoking, previous alcohol dependence, body mass index, and diastolic hypertension on the alcohol-CDT dose-response curve.
Can a blood test show heavy drinking? ›The short answer is yes: blood testing can show heavy alcohol use. However, timing plays a significant role in the accuracy of blood alcohol testing. In a typical situation, blood alcohol tests are only accurate six to 12 hours after someone consumes their last beverage.
What is a normal CDT level? ›The normal value of the serum CDT concentration is under 60 mg/liter; a value between 60 and 100 mg/liter indicates probable alcoholism, and a value > 100 mg/liter indicates a very high probability of alcoholism (specificity: 99%). Its sensitivity ranges from 60 to 91%, and its specificity ranges from 92 to 100%.
How does a PEth test work? ›What is PEth Testing? A PEth blood test measures the level of phosphatidylethanol, a direct alcohol biomarker which is found in human blood following alcohol consumption. Phosphatidylethanols are abnormal phospholipids formed in the presence of ethanol (more commonly known as alcohol).
What is involved in a medical examination for DVLA? ›The DVLA medical examination will consist of a medical questionnaire, a CDT blood test and any further tests deemed appropriate.
What is CDT alcohol test? ›CDT quantitation is useful in detecting abusive alcohol consumption (defined as ethanol consumption >40 mL per day for at least two weeks) and a more specific marker for alcohol exposure than other available markers, such as γ-glutamyl transferase (GGT).
What does a DVLA blood test look for? ›
Assessments look for: GGT (Gamma GT) - Gamma-glutamyl transferase is an enzyme from the liver. High levels can indicate alcohol abuse. MCV (Mean Cell Volume) - mean corpuscular volume (size) of the red blood cells.
Does iron lower CDT levels? ›In nonabusers, iron supplementation therapy significantly decreased CDT levels in patients with iron deficiency anemia (33.7 +/- 6.6 U/L vs. 21.7 +/- 5.2 U/L; P =. 0007), while iron-depletion treatment significantly increased CDT levels in patients with GH (9.7 +/- 2.0 U/L vs.
Should I fast before a CDT test? ›Preparation: Overnight fasting is preferred.
Do drugs affect CDT levels? ›Although drugs could theoretically affect CDT, few studies have investigated the role of pharmacological therapy on CDT levels (7); in particular, while enzyme-inducing antiepileptic drugs were reported to increase CDT, angiotensin II receptor antagonists (sartans) have been shown to lower CDT values (3, 8) .
Will liver enzymes be elevated after a night of drinking? ›The researchers also found that even a single episode of binge drinking elevated the levels of the liver enzyme CYP2E1, which metabolizes alcohol into toxic by-products that can cause oxidative damage and other forms of tissue injury.
Can drinking alcohol the night before a blood test affect liver enzymes? ›A gamma-glutamyl transferase (GGT) test helps diagnose liver disease. GGT is an enzyme in the liver that helps it work effectively. A person may need to avoid all eating and drinking for 8 hours before the test, as well as avoid drinking alcohol and taking some prescription medications.
Can one glass of wine raise liver enzymes? ›This study demonstrates that even very modest levels of alcohol intake can significantly affect liver enzymes and the most sensitive measure of alcohol intake is the enzyme GGT which is potentiated by alcohol intake as low as 7–14 g/day.