Carbohydrate-deficient transferrin, usually called CDT, is a blood test that can help identify sustained heavy alcohol use over the past several weeks. It is not a test for one recent drink, a hangover, or legal intoxication. Instead, CDT reflects changes in transferrin, an iron-transport protein made by the liver, when alcohol exposure repeatedly interferes with normal protein processing.
A high CDT result can support a pattern of harmful alcohol intake, especially when it fits the history and other blood markers such as GGT, AST, ALT, bilirubin, albumin, and INR. A normal CDT result does not rule out alcohol use disorder, binge drinking, or liver injury. The test is most useful when interpreted as one piece of a larger picture: drinking pattern, liver risk, medications, symptoms, and other lab results.
- CDT measures alcohol-related changes in transferrin, a liver-made protein that carries iron in the blood.
- A high CDT most often suggests repeated heavy alcohol intake, usually over 1–3 weeks or longer, not a single episode.
- Many modern methods use a cutoff near 1.7%–1.8% CDT, but the correct normal range is the one printed on the lab report.
- CDT often falls toward normal after about 2–4 weeks of abstinence, although timing varies by starting level and test method.
- False positives and false negatives can happen, especially with transferrin variants, some liver conditions, pregnancy, and method differences.
- CDT is not a liver function test, so abnormal liver enzymes or liver symptoms need separate medical evaluation.
Table of Contents
- What the CDT Test Measures
- When CDT Testing Is Used
- Normal Range and Result Meaning
- How Alcohol Patterns Affect CDT
- CDT and Liver Risk
- CDT Compared With Other Alcohol Markers
- False Results and Limitations
- What to Do After an Abnormal Result
What the CDT Test Measures
CDT stands for carbohydrate-deficient transferrin. Transferrin is a protein made mainly by the liver. Its usual job is to carry iron through the bloodstream. Like many proteins, transferrin normally has carbohydrate side chains attached to it. These side chains include sialic acid, a small sugar-related molecule that helps shape the final transferrin form.
With repeated heavy alcohol exposure, the liver may release more transferrin molecules that are missing some of these carbohydrate or sialic acid parts. These altered forms are grouped under the name carbohydrate-deficient transferrin.
Most CDT reports do not simply count one molecule. They measure a pattern of transferrin forms and often report the result as a percentage of total transferrin. This is commonly written as %CDT. Reporting CDT as a percentage helps reduce the effect of having naturally higher or lower total transferrin levels.
CDT is considered an indirect alcohol biomarker. That means it does not measure alcohol itself. It measures a body response that often happens after sustained alcohol exposure. This makes CDT different from blood alcohol concentration, which reflects alcohol currently circulating in the blood.
CDT also differs from routine liver enzymes. ALT, AST, ALP, bilirubin, and GGT can rise for many liver, bile duct, muscle, medication, and metabolic reasons. CDT is more focused on a heavy-drinking pattern, although it still has limitations.
A useful way to think about CDT is this: it is a pattern marker, not a moment marker. It usually becomes informative after repeated heavy drinking over time. It is much less useful for asking, “Did someone drink last night?”
For broader liver interpretation, CDT is often reviewed alongside a liver function tests panel, especially when the result is being used to understand possible alcohol-related liver stress.
When CDT Testing Is Used
CDT testing is most often used when a clinician needs more objective information about sustained heavy alcohol intake. It may be ordered in medical care, addiction treatment, transplant evaluation, workplace or safety-sensitive settings, legal or forensic contexts, or follow-up after counseling or treatment.
In routine medical care, CDT may be considered when liver enzymes are abnormal and the cause is unclear. For example, a person may have a high GGT, an AST/ALT pattern that raises concern for alcohol-related injury, fatty liver on imaging, or symptoms that suggest liver disease. CDT can help support or weaken the possibility that alcohol is contributing, but it should not be used as a stand-alone judgment.
CDT can also help in monitoring change over time. If CDT is high and then falls after a period of abstinence or major reduction, that pattern can support reduced alcohol exposure. If it rises again, it may suggest relapse or renewed heavy drinking, although confirmation with history and sometimes other biomarkers is still important.
Common uses include:
- Evaluating unexplained liver enzyme changes when alcohol may be a factor
- Supporting assessment of possible alcohol use disorder
- Monitoring abstinence or reduced drinking during treatment
- Reviewing alcohol exposure before liver transplant evaluation or major medical decisions
- Adding objective data when self-reported intake is uncertain
- Distinguishing some alcohol-related patterns from nonalcohol causes of liver test abnormalities
CDT is less useful for low-level drinking, occasional binge drinking, or recent isolated drinking. Someone can have a normal CDT and still drink in a way that is medically risky, especially if the pattern is intermittent rather than daily or near-daily.
In people with suspected alcohol-related liver injury, CDT is often interpreted with GGT and ALT patterns or with an AST/ALT ratio and GGT when the clinician is trying to separate alcohol-related stress from other liver problems.
Normal Range and Result Meaning
The normal range for CDT depends on the laboratory method. Many modern methods that report %CDT use a cutoff around 1.7% to 1.8%. Some older or different assay systems use higher cutoffs, such as around 2.6%, or report results in units rather than percent. The safest interpretation is always based on the reference interval printed beside the result.
A report may show:
| CDT pattern | Possible meaning | Important caution |
|---|---|---|
| Within the lab’s reference range | No laboratory evidence of sustained heavy alcohol intake during the usual detection window | Does not rule out binge drinking, alcohol use disorder, or liver disease |
| Borderline or slightly high | May reflect recent sustained intake, method variation, or an interfering condition | Often needs repeat testing and review with other markers |
| Clearly high | More supportive of repeated heavy alcohol exposure, especially if other findings fit | Still not diagnostic by itself |
| Falling on repeat testing | Can support reduced alcohol intake or abstinence | Timing depends on starting level and transferrin biology |
A low CDT result is usually not treated as a medical problem. Unlike some markers where a low value can suggest deficiency or organ dysfunction, low CDT generally means the measured alcohol-related transferrin pattern is not elevated. It does not mean a person has no liver risk from other causes.
A high CDT result should be read as evidence, not a final diagnosis. It can support recent sustained heavy alcohol use, but the clinician still has to consider the person’s history, symptoms, medications, pregnancy status, transferrin variants, and other lab results.
CDT results may be reported with wording such as “negative,” “normal,” “positive,” “abnormal,” or “consistent with heavy alcohol consumption.” The more useful number is the actual value, the unit, the reference range, and whether the same method is used for repeat testing.
When monitoring change, try to use the same laboratory and method. A change from 3.2% to 2.1% at the same lab is easier to interpret than a change between two different testing systems.
How Alcohol Patterns Affect CDT
CDT usually rises with sustained heavy drinking rather than occasional or light drinking. Many clinical descriptions associate a positive CDT with alcohol intake roughly in the range of 50–80 grams of ethanol per day for one to several weeks, although there is wide variation between people.
In the United States, one standard drink contains about 14 grams of pure alcohol. That means 56 grams is about four standard drinks, and 84 grams is about six standard drinks. In many other countries, a “standard drink” may contain 8, 10, 12, or more grams of alcohol, so grams are more precise than drink counts.
CDT is less sensitive when drinking is:
- Intermittent rather than daily or near-daily
- Heavy only on weekends
- Below the person’s CDT response threshold
- Recent but too brief to change transferrin patterns
- Reduced for several weeks before testing
CDT also does not rise in everyone who drinks heavily. Some people are “low responders,” meaning their CDT remains normal despite clinically important alcohol intake. Others may show a stronger rise at similar intake levels.
After alcohol intake stops, CDT generally falls gradually. A common clinical estimate is that CDT can return toward normal after about 2–4 weeks of abstinence. Very high starting levels may take longer. A borderline elevation may normalize sooner. The decline is not instant because transferrin proteins circulate for days before they are cleared and replaced.
The timing makes CDT useful for medium-term monitoring. For very recent drinking, urine ethyl glucuronide or ethyl sulfate may be more informative. For alcohol exposure across the past few weeks, PEth blood testing may be more sensitive in many settings. For current intoxication, an ethanol blood test is the direct test.
CDT and Liver Risk
CDT is connected to liver health because transferrin is made by the liver and because sustained heavy alcohol intake can injure the liver. Still, CDT is not a liver function test. It does not measure how well the liver is making albumin, clearing bilirubin, processing bile, or supporting clotting factors.
A high CDT mainly points toward an alcohol exposure pattern that may raise the risk of fatty liver, steatohepatitis, fibrosis, cirrhosis, pancreatitis, high blood pressure, sleep problems, neuropathy, and several cancers. The liver risk depends on more than the CDT number. Duration of drinking, binge pattern, sex, body weight, diabetes, viral hepatitis, genetics, nutrition, medications, and metabolic health all matter.
Alcohol-related liver injury often shows up through other tests before symptoms appear. These may include high GGT, AST, ALT, bilirubin, alkaline phosphatase, ferritin, INR, or low albumin and platelets in more advanced disease. CDT can help identify alcohol as one contributor, but it cannot stage liver damage.
A pattern that may raise concern for alcohol-related liver injury includes:
- High CDT plus high GGT
- AST higher than ALT, especially when the AST/ALT ratio is elevated
- High bilirubin or jaundice
- Low albumin or high INR
- Low platelets, enlarged spleen, or signs of portal hypertension
- Ultrasound or elastography evidence of fatty liver or fibrosis
If fibrosis risk is part of the concern, clinicians may calculate scores such as FIB-4 or APRI using routine labs. These scores do not diagnose alcohol intake, but they help estimate the chance of significant liver scarring. A separate article on FIB-4 and APRI liver fibrosis scores can help explain how those calculations fit into liver follow-up.
CDT can be normal in advanced liver disease, and it can be abnormal without advanced liver disease. That is why the result should not be used to reassure someone that the liver is safe or to diagnose cirrhosis. If there are symptoms such as jaundice, vomiting blood, black stools, confusion, severe abdominal swelling, easy bruising, or worsening weakness, medical care should not wait for CDT interpretation.
CDT Compared With Other Alcohol Markers
Alcohol-related testing can measure different time windows. Some tests detect alcohol itself. Some detect alcohol breakdown products. Others detect body changes caused by repeated exposure. CDT belongs to the last group.
| Marker | What it reflects | Usual strength | Main limitation |
|---|---|---|---|
| Blood, breath, or urine ethanol | Current or very recent alcohol presence | Best for intoxication or immediate exposure | Short detection window |
| EtG and EtS | Recent alcohol metabolites | Useful for recent drinking over the past few days | Can be affected by incidental exposure and cutoff choice |
| PEth | Alcohol-specific phospholipid formed in blood cells | Often sensitive for repeated drinking over several weeks | Cutoffs and interpretation vary by setting |
| CDT | Alcohol-related transferrin pattern | More specific for sustained heavy intake than many routine enzymes | Can miss intermittent drinking and some heavy drinkers |
| GGT | Liver and bile duct enzyme induction or injury | Common, inexpensive, often rises with alcohol exposure | Also rises with fatty liver, medications, cholestasis, and other causes |
| AST and ALT | Liver cell injury, and sometimes muscle injury | Helpful for liver inflammation patterns | Not alcohol-specific |
| MCV | Average red blood cell size | May rise with chronic heavy alcohol use | Also affected by B12, folate, thyroid disease, liver disease, and marrow disorders |
CDT often performs better than GGT or MCV for identifying sustained heavy drinking because it is less likely to rise from common nonalcohol causes. However, it is not the most sensitive alcohol marker for every situation. PEth has become widely used because it is more directly linked to ethanol exposure and can detect a broader range of repeated drinking patterns.
GGT remains useful because it is widely available and also tells clinicians about liver and bile duct stress. A high GGT with high CDT gives stronger support for alcohol-related exposure than either test alone. A high GGT with normal CDT may point toward fatty liver, medications, bile duct disease, metabolic syndrome, or alcohol intake below the CDT detection threshold.
AST and ALT help assess liver cell injury. In alcohol-related liver disease, AST is often higher than ALT, but this pattern is not perfect. Muscle injury, advanced fibrosis, medications, viral hepatitis, and metabolic liver disease can blur the pattern. A general article on ALT and AST interpretation may help when liver enzymes are part of the same lab panel.
No alcohol biomarker should be used in isolation to label a person. A careful interpretation combines the test result with timing, drinking history, medical conditions, and the reason the test was ordered.
False Results and Limitations
CDT can produce misleading results. Some problems come from biology, and some come from the testing method.
False positives are uncommon with well-standardized methods, but they can happen. Possible causes include genetic transferrin variants, rare congenital disorders of glycosylation, some advanced or unusual liver diseases, pregnancy-related changes, and analytical interference. Some methods are better than others at detecting transferrin variants that could distort the result.
False negatives also happen. A person may drink heavily but still have a normal CDT if the drinking period is too short, the pattern is intermittent, the amount is below that person’s response threshold, or the person is a weak CDT responder. CDT may also fall after several weeks of abstinence or reduced intake, even if alcohol caused earlier harm.
Method differences matter. High-performance liquid chromatography, capillary electrophoresis, immunoassays, and other approaches may define and measure CDT somewhat differently. This is one reason the reference interval must come from the performing lab.
Common interpretation mistakes include:
- Treating CDT as proof of current intoxication
- Assuming a normal CDT rules out alcohol-related harm
- Comparing results from different labs as if they were identical
- Ignoring transferrin variants or unusual liver disease
- Reading a borderline result without repeat testing
- Using CDT to judge liver scarring, which it cannot measure
A borderline CDT result is often the hardest to interpret. It may represent early or moderate elevation, laboratory variation, a falling level after reduced intake, or an interfering factor. Repeat testing after a defined period, ideally with the same lab, can provide more information than one isolated number.
CDT can also be emotionally charged. People may feel accused, embarrassed, defensive, or worried about the result. A medical interpretation should stay factual: what the test can show, what it cannot show, and what additional information is needed.
What to Do After an Abnormal Result
An abnormal CDT result deserves a calm review rather than panic. The next step depends on why the test was ordered and what the rest of the medical picture shows.
Start with the lab report. Check the unit, reference range, method if listed, and whether the result is mildly or clearly elevated. Then compare it with the timing of alcohol intake, any recent period of abstinence, pregnancy status, known liver disease, iron-related conditions, and prior CDT results.
A clinician may review:
- Alcohol pattern in grams or standard drinks per day and per week
- Binge episodes and alcohol-free days
- Symptoms of withdrawal, cravings, or loss of control
- Liver enzymes, bilirubin, albumin, INR, CBC, platelets, and ferritin
- Medications and supplements that may affect liver tests
- Viral hepatitis risk, metabolic syndrome, diabetes, and obesity
- Imaging or fibrosis assessment when liver disease is suspected
If the CDT result supports heavy alcohol exposure, reducing or stopping alcohol can lower medical risk. People who drink daily or heavily should not always stop suddenly without medical advice. Alcohol withdrawal can be dangerous, especially in people with prior seizures, hallucinations, severe tremor, high daily intake, or other major illness. In those situations, supervised withdrawal planning is safer.
For liver follow-up, CDT is only one part of the plan. A clinician may order a hepatic function panel, CBC, INR, GGT, ferritin, hepatitis testing, ultrasound, elastography, or fibrosis scores. If albumin is low or INR is high, that points more directly toward impaired liver synthetic function. A deeper discussion of albumin and INR in liver synthetic function can help explain why those markers carry different meaning than CDT.
Repeat CDT testing may be useful after 2–4 weeks if the goal is monitoring. A falling result can support reduced drinking. A persistently high or rising result may mean continued heavy intake, relapse, or an interfering issue that needs review.
Medical care is more urgent when abnormal CDT appears with jaundice, confusion, severe abdominal swelling, vomiting blood, black stools, fainting, fever with abdominal pain, or easy bleeding. Those symptoms can signal serious liver or gastrointestinal complications and need prompt evaluation.
References
- Carbohydrate-deficient transferrin as a marker of chronic alcohol abuse: a critical review of preanalysis, analysis, and interpretation 2001 (Review)
- Carbohydrate-deficient transferrin (CDT) as a marker of alcohol abuse: a critical review of the literature 2001-2005 2006 (Review)
- Monitoring of the Alcohol Biomarkers PEth, CDT and EtG/EtS in an Outpatient Treatment Setting 2012 (Clinical Study)
- Phosphatidylethanol Compared with Other Blood Tests as a Biomarker of Moderate Alcohol Consumption in Healthy Volunteers: A Prospective Randomized Study 2015 (RCT)
- Consensus for the use of the alcohol biomarker phosphatidylethanol (PEth) for the assessment of abstinence and alcohol consumption in clinical and forensic practice (2022 Consensus of Basel) 2022 (Consensus Statement)
- ACG Clinical Guideline: Alcohol-Associated Liver Disease 2024 (Guideline)
Disclaimer
CDT results should be interpreted by a qualified healthcare professional in the context of symptoms, alcohol history, medications, pregnancy status, liver tests, and the laboratory method used. A high CDT result can support sustained heavy alcohol exposure, but it does not diagnose liver damage by itself. People who drink heavily should seek medical advice before stopping suddenly because alcohol withdrawal can be dangerous.
