CDT Test (for alcohol misuse)

CDT Test (carbohydrate deficient transferrin) is a blood test used to check if a person has been drinking excessive quantities of alcohol over the previous 7-14 days.

CDT is a normal protein in the body and is present in all people. It only becomes elevated when a person drinks excessive amounts of alcohol regularly or even with binge drinking.

A CDT test is used by the DVLA when a person applies for their driving license to be reinstated. The DVLA accepts a CDT cut-off level of ≤ 2.2 %. A CDT test is also used by companies, such as Transport for London (TfL), who want to make sure an employee is not drinking excessively.

In our experience, the DVLA CDT tests can cause a lot of anxiety. Many of our clients order their own CDT test for for their own piece of mind before they attend for their official DVLA assessments. 

Alcohol in urine or blood can only be detected for 24-48 hours. Therefore, a CDT test is a better test for alcohol misuse because it checks a longer time-frame. An Alcohol Profile test is even better because it checks for changes in the blood and liver to assess the adverse effects of alcohol.

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Proof of ID:

You should bring with you a valid photo ID such as a passport or driving license. No copies or mobile images are accepted. 

Results:

Results take 5 working days * and will be emailed to you. They include a doctor's explanation of the results. Please note that we do not give out results by telephone as this information is confidential and there is no way of identifying a caller.

* Indicative timings only. Actual result may be earlier or slightly later.

   Often combined with a liver function blood test to check for any damage to the liver from excessive alcohol consumption.

> Do a home CDT Test

 Causes of a high CDT level:

1. Alcohol Misuse (A 19 out of 20 chance): i.e. by far the most likely cause of a high CDT.

2. Liver Disease: Certain liver problems which cause a blockage or damage to bile ducts; e.g. primary biliary cirrhosis, primary sclerosing cholangitis, gallstones or liver/pancreatic cancer. These causes can be excluded if liver function tests (LFTs) are normal.

3. Transferrin Variants: Transferrin is a protein used to transport iron and can undergo changes by the consumption of alcohol. The normal type is C. People who have type D may have a raised CDT. Type D is rare in Caucasians but may be present in 10% of Africans. People with this variant cannot use CDT to check for alcohol misuse because CDT will always be high. We would recommend that these clients use a urine EtG test instead.

4. Carbohydrate deficient glycoprotein syndromes: these are very rare syndromes resulting in mental retardation in children.

How much alcohol will cause a high CDT level?

You need to drink the equivalent of 100-150g of alcohol per day to raise CDT levels. This equates to 5 pints of beer, a bottle of wine, or one-third of a bottle of spirits daily.

Intermittent or "binge" drinking can also raise CDT levels. This would have to be in the range of 200-300g of alcohol on two occasions per week (around double the above amount) and no alcohol on the other days. Just one day of excessive drinking with the other days of no alcohol would probably not be enough to raise CDT levels over a 7-14 day period.

Notes from the DVLA website

High risk offenders with alcohol problems

Defined in terms of the alcohol-related driving convictions below, the courts notify the DVLA of high risk offenders.

An independent medical examination will be arranged when an application for licence reinstatement is received by the DVLA. The assessment includes:

• questionnaire
• serum CDT assay
• any further testing indicated.

If a licence is awarded, the ’til 70 licence is restored for Group 1 car and motorcycle driving. Consideration may be given to a Group 2 licence.

If a high risk offender has a previous history of alcohol dependence or persistent misuse but has satisfactory examination and blood tests, a short period licence is issued for ordinary and vocational entitlement but is dependent on their ability to meet the standards as specified.

A high risk offender found to have a current history of alcohol misuse or dependence and/or unexplained abnormal blood test results will have the application refused.

Definition

The high risk offender scheme applies to drivers convicted of the following:

• one disqualification for driving or being in charge of a vehicle when the level of alcohol in the body equalled or exceeded either one of these measures:
  • 87.5 mcg per 100 ml of breath
  • 200.0 mg per 100 ml of blood
  • 267.5 mg per 100 ml of urine
• two disqualifications within the space of 10 years for drinking-driving or being in charge of a vehicle while under the influence of alcohol
• one disqualification for refusing or failing to supply a specimen for alcohol analysis
• one disqualification for refusing to give permission for a laboratory test of a specimen of blood for alcohol analysis.