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Doctor's Assessment Included

Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

Drug Screening

CDT (Carbohydrate-Deficient Transferrin)

A CDT blood test measures carbohydrate-deficient transferrin, a biomarker that indicates chronic heavy alcohol consumption over the preceding weeks. CDT is considered one of the most specific markers for sustained excessive alcohol intake.

What It Measures

This test measures the proportion of carbohydrate-deficient transferrin (CDT) in the blood. Transferrin is a protein that transports iron in the bloodstream. Chronic heavy alcohol consumption alters the glycosylation pattern of transferrin, resulting in an increase in carbohydrate-deficient isoforms.

Elevated CDT levels typically reflect sustained heavy drinking over approximately 2 to 3 weeks. CDT is not significantly affected by acute or occasional alcohol use.

Why It Matters

CDT testing provides objective evidence of chronic heavy alcohol consumption that other alcohol markers may not capture. Unlike EtG, which detects recent alcohol exposure, CDT reflects a pattern of sustained heavy drinking over weeks.

This makes CDT particularly valuable for treatment programme compliance monitoring, licence reinstatement evaluations, and clinical assessments where a longer-term drinking pattern is relevant.

When to Test

Testing may be relevant for monitoring alcohol treatment programme compliance, clinical assessment of suspected chronic alcohol use, occupational health evaluations, and licence reinstatement processes.

Consult a healthcare professional for guidance on when CDT testing is appropriate and how to interpret results in the appropriate clinical or regulatory context.

Frequently Asked Questions

What drinking pattern does CDT reflect?
CDT levels become elevated after approximately 2 to 3 weeks of sustained heavy alcohol consumption, generally defined as more than 60 grams of alcohol per day. CDT is not typically elevated by occasional or moderate drinking.
How accurate is CDT as an alcohol marker?
CDT is considered one of the most specific biomarkers for chronic heavy drinking, with high specificity. However, certain conditions such as advanced liver disease, genetic variants, and pregnancy may affect CDT levels. Clinical context is important for interpretation.
What should I expect from a CDT blood test?
The test involves a standard blood draw. The sample is analysed to determine the proportion of carbohydrate-deficient transferrin. Results are typically reported as a percentage, with values above the reference range indicating likely chronic heavy alcohol consumption.

Test Products

This marker is included in the following test panels.