CDT Test (for alcohol Misuse) - Self-Collect and Post
This home CDT test (carbohydrate deficient transferrin) is a blood test used to check if a person has been drinking large amounts 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 their own piece of mind before they attend for their official DVLA assessments.
A CDT test has an advantage over testing for alcohol in urine or blood which is only detectable for 24-48 hours. For the purposes of detecting alcohol misuse, it is not recommended to use only a CDT test. It would be better to also do other tests such as MCV and liver function tests as in our Alcohol Profile.
Please make sure that your address details are correct at the time of ordering the test. A CDT self-collection kit containing clear instructions and testing equipment will then be posted to you.
The blood sample for the CDT test is taken by pricking your finger with a small sharp lancet. These are the same sort of small needles that are used by diabetics when they are checking their blood sugar.
Please watch this video showing how this is done, before trying to collect the sample. Written instructions can be found here. Only a small amount of blood is needed but some samples may be rejected by the laboratory because there is not enough.
You can then post the blood sample for the CDT test in the postage-paid plastic envelope that we provide. Please allow time for this to reach the laboratory.
Results available: 5 working days after arrival at the laboratory * (Please allow time for delivery). Clients should order their home test kits at least 2 weeks before they need the results to avoid potential problems.
CDT test results are usually available within 5 working days of reaching the laboratory and will be e-mailed to you with a doctor's explanation of what the result means.
* Indicative timings only. Actual result may be earlier or slightly later.
Causes of a high CDT level:
1. Alcohol Misuse (A 19 out of 20 chance): i.e. by far the most likely cause
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 raise the level of CDT?
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.
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:
- 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.
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.