Carbohydrate Deficient Transferrin (CDT) DVLA Blood Test, from our experts to you.
Dr Natasha Fernando MBBS, MRCGP

Medical Director

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What does the
CDT DVLA Blood Test measure?

Our CDT DVLA Blood Test measures transferrin, a particularly sensitive biomarker that tracks heavy alcohol consumption over an extended period. Transferrin is a protein that carries iron to parts of the body that need it. Drinking too much alcohol can cause an increase in certain types of transferrin which are deficient in carbohydrates. Intermittent or binge drinking can also increase CDT levels, which depends on the frequency of binges and the amount of alcohol consumed on each occasion. Elevated CDT will decline with reduced alcohol consumption and revert to normal after several weeks of abstinence.

Can other substances
affect my results?

This test has a very high level of specificity (i.e. it is not affected by other drugs or substances). That's why the Secretary of State's Honorary Medical Advisory Panel has adopted it as the sole test for assessing the harmful use of alcohol for high-risk offenders.

What can I learn
from this test?

You can use this rest to show that you have stopped or reduced your alcohol consumption or to see if you will pass the DVLA medical. If you drink steadily and heavily (four-six units of alcohol per day) for several weeks, the percentage of transferrin that is deficient in carbohydrates will rise. The longer you drink at this level, the higher the level of CDT.

Our test is analysed using a different method from the official DVLA laboratory. It will not be possible to get a result for around 2% of people taking this test due to a normal genetic variant in transferrin. If this applies to you, an alternative test will be recommended.

What's Included?

Alcohol consumption
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Carbohydrate deficient transferrin 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.