Metals, toxins and medication
CDT
A form of the iron transport protein transferrin that increases with prolonged heavy drinking in the past weeks.
Everything about this testWhat it measures
Transferrin is the protein that carries iron through the blood. Transferrin has sugar chains attached; under the influence of a breakdown product of alcohol, more forms appear in which such a chain is missing. This is carbohydrate-deficient transferrin, CDT for short. The result is given as a percentage of all transferrin, so that fluctuations in the total amount of transferrin do not affect it. CDT is never zero: even without alcohol use, there is always a small amount.
- Prolonged heavy drinking in the weeks before the blood draw
- Monitoring a period without alcohol: with abstinence, the value falls again
High
A raised CDT value fits heavy drinking for at least a week. According to the Dutch medical specialists' guideline (FMS) on fitness to drive, a result above 2.0 percent (standardized as CDT IFCC) counts as a sign of excessive drinking; a slightly raised value below that does not. According to the Dutch Society for Clinical Chemistry (NVKC), a raised value in men roughly corresponds to an average of 60 grams of alcohol per day or more, and in women to about 40 grams per day. There are also other causes of a slightly raised value: advanced liver disease, the second half of pregnancy and an inherited variant of transferrin. After stopping alcohol, CDT usually returns to normal within two to three weeks; after years of heavy drinking, this can take longer.
Low
A normal CDT value makes prolonged heavy drinking less likely, but does not rule it out. This is because the test has low sensitivity: in the studies in the 2020 FMS guideline, 36 to 51 percent of people with excessive drinking were detected. Drinking less than about 40 grams of alcohol per day in men and 30 grams in women does not give a raised value. Someone who drinks heavily but stopped a few weeks before the sample collection can also have a normal result.
If your result is abnormal
With a raised value, the GP looks together with you at your alcohol use and at other causes, and usually has liver values measured. A repeat measurement often follows after a few weeks of cutting down or stopping, because CDT should then fall. With a persistently raised value without an explanation, further testing of the liver or for a transferrin variant may be needed.
Reliability
According to the Dutch medical specialists' guideline (FMS), CDT is the most suitable laboratory value for showing prolonged heavy drinking: the specificity is high, the sensitivity low. This means that a clearly raised value says a lot, and a normal value says little. The result is reported as CDT IFCC, standardized to an international reference method.
Limitations
- An inherited variant of transferrin makes the CDT percentage unreliable; the result then cannot be interpreted.
- Advanced liver disease and the second half of pregnancy can slightly raise the value; different limits apply during pregnancy.
- Timing matters: after two to three weeks without alcohol, the value is usually normal again, so recently stopping strongly affects a result.
- There are different measurement methods (HPLC, capillary electrophoresis, N-Latex) with their own limits; only results standardized to them can be compared with each other.
How common is this
In 2025, 5.5 in 100 adults in the Netherlands drank excessively: more than 21 glasses per week for men, more than 14 glasses for women. In men this is 7.4 in 100 and in women 3.7 in 100. By no means everyone who drinks excessively has a raised CDT, because the value only rises with heavy amounts.
Who is this useful for
Useful if you want to see whether your alcohol use in the past weeks was so high that it shows up in the blood, for example when cutting down or stopping, and as an addition to gamma-GT. The test is not intended to check someone else's alcohol use and says nothing about whether there is dependence; that is assessed in a conversation with a doctor.
Downsides and risks
- A raised result is quickly seen as proof of an alcohol problem, while liver disease, pregnancy or an inherited transferrin variant may be the cause.
- A normal result says little: heavy drinking can go unnoticed, and the value is no proof of abstinence.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results