Carbohydrate-Deficient Transferrin
The CDT test quantifies carbohydrate-deficient transferrin isoforms, the most specific biomarker of sustained heavy alcohol consumption. CDT rises with daily intake above 50–80 g over two or more weeks and falls with abstinence, making it invaluable for distinguishing alcohol-related liver injury from other causes and for monitoring treatment compliance.
1
Biomarkers
Blood (serum)
Sample
2–4 business days
Turnaround
No
Fasting
What is the CDT test?
The Carbohydrate-Deficient Transferrin test quantifies the proportion of undersialylated transferrin isoforms in serum, a biochemical footprint of prolonged heavy alcohol consumption. It occupies a unique niche among alcohol biomarkers: less sensitive than GGT or MCV to occasional drinking but far more specific, rising reliably in sustained intake and falling predictably with abstinence. Clinicians order CDT when objective evidence of chronic alcohol use is needed — to corroborate a clinical suspicion, to motivate engagement with treatment, to monitor compliance in abstinence or harm-reduction programmes, or to distinguish alcohol as the cause of liver enzyme elevations. Because CDT responds to the pattern and volume of drinking over weeks rather than to single episodes, it reflects the heavy sustained use that drives organ damage, and its decline with sobriety provides measurable feedback in recovery pathways.
What does the CDT test measure?
Transferrin is a plasma glycoprotein synthesised by the liver that carries iron and is normally decorated with branched oligosaccharide chains terminating in sialic acid residues. Chronic heavy alcohol consumption interferes with the glycosylation machinery in hepatocytes, resulting in undersialylated (carbohydrate-deficient) isoforms — predominantly asialo- and disialo-transferrin. These isoforms rise after sustained alcohol intake over several days to weeks and fall with a half-life of approximately two weeks after cessation, making CDT a marker of the chronicity and quantity of drinking rather than a snapshot of recent intake.
CDT is the most specific biomarker of chronic heavy alcohol consumption in routine clinical use. It is less sensitive to isolated binge episodes than GGT or MCV but much more specific: it rises almost exclusively in response to sustained ethanol intake, with few non-alcohol causes. Practitioners employ CDT to screen for and monitor alcohol use disorder, to support abstinence programmes, and to distinguish alcohol-related liver injury from other causes when aminotransferases and GGT are elevated.
Why is the CDT test ordered?
- Evaluation of suspected chronic alcohol use disorder when history is unreliable or denied and objective corroboration is required
- Monitoring abstinence or reduced consumption in patients engaged in alcohol treatment or harm-reduction programmes
- Distinguishing alcohol-related liver injury from viral, autoimmune, or metabolic causes when GGT and aminotransferases are elevated
- Pre-operative risk assessment for elective surgery when unrecognised heavy drinking may increase peri-operative morbidity
- Occupational or medico-legal contexts requiring objective demonstration of abstinence or of chronic heavy use
- Screening high-risk populations — patients with depression, hypertension, or metabolic syndrome — in whom alcohol intake is underreported
- Follow-up after an initial positive result to document trend with treatment or to confirm the specificity of an isolated elevation
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
2–4 business days
Collection notes
Phlebotomy via LabCorp patient service centre or Access Medical Laboratories draw site; no special preparation. Avoid collection immediately after blood transfusion or during acute haemolysis. Note the performing laboratory for serial comparability, as assay methods and cut-offs differ.
Specimen requirements
Minimum 1.0 mL serum (gel separator acceptable). Separate from cells promptly; CDT is stable refrigerated for several days and frozen for longer-term storage. Immunoassay or capillary electrophoresis methods are laboratory-dependent; verify the assay type for serial monitoring.
What can affect CDT results?
Inherited defects in N-glycan assembly produce carbohydrate-deficient glycoproteins, including transferrin; these are rare paediatric syndromes and are differentiated by clinical presentation and isoform pattern.
Advanced liver disease can impair glycosylation, occasionally raising CDT independently of alcohol; correlate with albumin, INR, and clinical context.
Women may show higher CDT values at equivalent alcohol intake because of differences in alcohol metabolism and body water distribution; sex-specific or adjusted thresholds improve specificity.
CDT requires roughly two weeks of daily intake above 50–80 g to rise appreciably, so it remains normal in episodic or moderate drinkers; this confers high specificity but lower sensitivity than GGT for occasional excess.
Hormonal changes can alter transferrin glycosylation and total transferrin concentration, potentially affecting the CDT percentage; interpret cautiously in these settings.
Marked iron deficiency increases total transferrin synthesis and may dilute the CDT fraction; transfusion alters iron status and transferrin turnover, so a stable steady state is preferred.
What do CDT results mean?
Elevated
Values above the laboratory threshold (typically >1.7–2.0%) indicate sustained heavy alcohol consumption — generally intake in excess of 50–80 g per day for at least two weeks. Very high CDT strongly supports chronic alcohol use disorder, and serial elevation despite reported abstinence suggests either continued drinking or the lag time required for clearance. Rare non-alcohol causes include congenital disorders of glycosylation and occasionally severe cirrhosis; clinical context and isoform pattern help differentiate.
Normal
A normal CDT in a patient with suspected alcohol misuse suggests either that intake has been episodic or below the threshold for glycosylation changes, or that sufficient abstinence time has elapsed for the isoforms to normalise. It does not rule out harmful drinking patterns that have not reached the chronicity to raise CDT, so correlation with GGT, MCV, and clinical assessment is essential.
Reduced
CDT within the normal range does not exclude alcohol use disorder if drinking is episodic or intake has been below the threshold needed to alter glycosylation. A falling CDT in a patient with previously elevated values is consistent with reduced intake or abstinence and provides objective encouragement in treatment.
Note: CDT is highly specific but only moderately sensitive: it may remain normal in non-daily or lower-volume drinkers whose use is nonetheless harmful. It should be read alongside GGT (which rises earlier but is less specific) and the clinical history. Female patients and those with altered iron status or advanced liver disease require cautious interpretation, and congenital glycosylation disorders, though rare, must be considered in atypical presentations.
Frequently asked questions
Elevated CDT indicates sustained heavy alcohol consumption, typically intake above 50–80 grams per day for at least two weeks. It is the most specific routine biomarker of chronic alcohol use and rarely rises for other reasons.
How to access the CDT test
The CDT reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Helander A, Wielders J, et al. Towards standardization of carbohydrate-deficient transferrin (CDT) measurements: II. Performance of a laboratory network running the HPLC candidate reference measurement procedure and evaluation of a capillary electrophoresis method. Clin Chem Lab Med. (2016)
- Arndt T. Carbohydrate-deficient transferrin as a marker of chronic alcohol abuse: a critical review of preanalysis, analysis, and interpretation. Clin Chem. (2001)
- European Association for the Study of the Liver. EASL clinical practice guidelines: management of alcohol-related liver disease. J Hepatol. (2018)
- National Institute for Health and Care Excellence (NICE). Alcohol-use disorders: diagnosis, assessment and management of harmful drinking and alcohol dependence (CG115). (2011)
- Conigrave KM, et al. CDT, GGT, and AST as markers of alcohol use: the WHO/ISBRA collaborative project. Alcohol Clin Exp Res. (2002)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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