Carbohydrate Deficient Transferrin (CDT) DVLA Blood Test


Measure the level of Carbohydrate Deficient Transferrin (CDT) in your blood, as tested by the DVLA in its fitness-to-drive test.

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Carbohydrate Deficient Transferrin (CDT) DVLA Blood Test

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Is it for you?

Do you need to take a DVLA fitness-to-drive test?

If you have lost your driver's licence due to problem drinking, but you're no longer drinking heavily or frequently, then this test can help you prove that your drinking is in the past.

By measuring CDT, you can monitor alcohol consumption over an extended period and be reassured that you would pass the DVLA fitness-to-drive test.

Biomarker table

Alcohol consumption

Carbohydrate deficient transferrin

Learn more

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.
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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 test 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 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.

How far back can a CDT test go?

The exact period of time of alcohol consumption covered by the CDT test cannot be determined. However, for a positive CDT result, an increase in alcohol intake for longer than 2-4 weeks prior to the test is required.

Research suggests that consuming 60–80 grams of alcohol per day for at least two to three weeks can increase CDT levels. CDT levels typically return to normal after around four weeks of abstinence.

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