Do you need to take a DVLA fitness-to-drive test? If you’ve lost your licence relating to alcohol, this test assesses your drinking patterns by measuring your CDT levels. Low CDT levels can help reassure you that you’re likely to pass the DVLA’s equivalent test.
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What's in the test?
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.
How to prepare for your test
Test limitations
A negative result indicates no recent chronic drinking but can't rule out binge drinking. It also doesn't guarantee passing the DVLA's fitness-to-drive test, which requires further proof of satisfactory recovery.
About one in 50 people won’t receive a result due to a genetic variation in transferrin. In this case, we’ll recommend an alternative test.
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FAQs
Can other substances affect my results?
This test has a very high level of specificity (i.e. it’s 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 chronic alcohol use.
What can I learn from this test?
This test can help show that you’ve not consumed excessive amounts of alcohol over the last few weeks. It measures the percentage of transferrin that is deficient in carbohydrate, which rises with persistent moderate-to-heavy drinking over a period of weeks. The longer you drink alcohol, the higher the percentage of CDT.
A low percentage (<1.7%) suggests no heavy drinking in the past few weeks.
About one in 50 people won’t receive a result due to a genetic variation in transferrin. In this case, we’ll recommend purchasing an alternative test.
What does the CDT DVLA Blood Test measure?
Our CDT DVLA Blood Test measures transferrin, a protein that carries iron in the blood. Drinking too much alcohol can cause transferrin to become deficient in carbohydrates, measured as a percentage.
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. Raised CDT levels will decline with reduced alcohol consumption and revert to normal after several weeks of abstinence.
How far back can a CDT test go?
A CDT test can detect heavy drinking (about 6-10 units/day) within a two-to-four-week window, but this varies according to the pattern of drinking.
CDT levels typically return to normal after around four weeks of abstinence.