Carbohydrate Deficient Transferrin Test

What is Carbohydrate Deficient Transferrin?

Serum transferrin is a glycoprotein (that’s protein linked to carbohydrate). It is produced in the liver and is the main transporter of iron in the blood. Transferrin occurs in several slightly different forms called isoforms. These isoforms differ in the number of carbohydrate side chains.

The main isoform present in the blood of healthy individuals is the tetrasialo isoform (with four side chains). However, individuals who consume alcohol frequently or who have recently consumed alcohol have higher levels of the asialo (no side chain), monosialo (one side chain), and disialo (two side chains) isoforms. Collectively, the asialo, monosialo, and disialo isoforms are known as carbohydrate deficient transferrin (CDT).

Can I buy a Carbohydrate Deficient Transferrin test online?

The Online Clinic offers this test with results in 3 days. Blood can be collected using a specially designed kit at home, or patients can attend a pharmacy to have blood drawn by a phlebotomist. All results are interpreted by a doctor, and you can ask questions if anything is unclear.

What is a Carbohydrate Deficient Transferrin test?

The CDT test is used to determine the level of alcohol in the blood. It does this by assessing the percentage of transferrin in the blood that is carbohydrate deficient (%CDT). Using %CDT means that the test is highly accurate as it avoids false high or false low results that may arise from very high or very low total transferrin concentrations.

The level of CDT in the blood can be greatly influenced by alcohol consumption. It seems that alcohol has a direct effect on the enzymes involved in adding/removing the transferrin side chains, i.e., inhibiting those that add side chains and stimulating those that remove side chains. This means that excessive and persistent alcohol consumption changes the proportions of the different isoforms, resulting in more of the isoforms making up CDT. In this way, CDT is an ideal indirect measure of alcohol consumption over a defined period.

A CDT test can be used to detect long-term excessive alcohol use for about four weeks before a blood sample is taken. However, CDT is not a good indicator of binge drinking or occasional excessive alcohol intake.

CDT test results may be affected by several factors, meaning false-positive tests may occur. CDT can be affected by factors including genetic variants, iron deficiency, liver disease, chronic illness, medications, female sex, menopausal status, during pregnancy and for eight weeks after birth. The results may, therefore, be assessed along with other observations/investigations.

Why is a Carbohydrate Deficient Transferrin test important?

CDT plays a key role in determining whether an individual has been drinking alcohol chronically and to excess over a set period of time. An increase in CDT is caused by consuming about 60–80 g/day for at least 10–15 days, with a return to normal levels after around 2–4 weeks of total alcohol abstinence.

Who should have their Carbohydrate Deficient Transferrin level tested?

Any person worried that alcohol may be impacting their health may use the CDT test to detect any potential issues early on. The test can also help to monitor the progress of those individuals who have or may have health conditions (e.g., liver disease, pancreatitis) caused by heavy drinking, although they are now abstaining from alcohol consumption.

Several professional groups may have cause to use a CDT test, such as:

• Doctors or specialists who wish to investigate an individual’s alcohol intake for any reason, including for those with alcohol dependency, at risk of alcohol misuse, with a history of heavy drinking, or whose progress is being monitored during treatment and recovery.
• The police and the Driver and Vehicle Licensing Agency (DVLA) use the CDT test to investigate alcohol levels in a driver’s blood. The test can be used to assess whether a driver should be disqualified from driving or is fit to drive before regaining their driving licence after being disqualified.
• Local authorities and legal bodies may require alcohol consumption assessments when determining the need for protection from harm by a family member or to guide decisions about a vulnerable individual’s care.

How to test for Carbohydrate Deficient Transferrin?

A few drops of blood are needed for the home CDT test, whereby you collect the blood sample yourself. A blood sample can also be collected from a vein in your arm by a healthcare professional.

If you collect the blood sample at home, then The Online Clinic provides a self-collection blood sample pack. The pack also contains instructions about how to collect the sample and packaging for sending the sample for laboratory analysis. Blood drops are collected from a little finger after using a lancet to pierce the skin. A blood collection tube is provided, and blood droplets are collected up to the marked upper line (600 mcl). Once sealed, the blood collection tube is gently inverted 5–10 times. The tube is then labelled with your details and mailed to the laboratory. Results are sent to The Online Clinic and a doctor will advise you on the findings.

What are normal Carbohydrate Deficient Transferrin test results?

Normally, CDT test results are less than 1.6%–1.7% of total transferrin, which indicates no recent chronic heavy alcohol consumption. Lower levels usually reflect moderate drinking or abstinence over the previous 1–2 weeks. Individuals with chronic heavy alcohol consumption or alcohol misuse usually have a higher percentage of transferrin as CDT (greater than 2%).

Generally, CDT levels will return to normal levels within 7–28 days, which is the time it takes for CDT to be cleared from the blood.

How to maintain normal Carbohydrate Deficient Transferrin levels

Since CDT is cleared from the body within one month, any excess intake of alcohol needs to fall within this time to return to normal levels.

In terms of health, no amount of alcohol consumption is without risk. According to the NHS guidelines for men and women, the health risks from alcohol are kept at a low level when drinking no more than 14 units per week on a regular basis. Intake should be spread over 3 or more days, with several alcohol-free days, and no binge drinking.

The following will help you to maintain normal CDT levels:

• In the UK, one unit is 10 ml or 8 g of pure alcohol.
• The number of units in a drink will depend on the strength of the alcohol and size of the drink.
• A drink’s alcohol content is expressed in terms of percentage alcohol by volume (%ABV), i.e., the volume of the drink that is pure alcohol.
• The number of units in a drink is calculated as follows: strength (%ABV) x volume (in ml) ÷ 1,000 = units.
• As a guide, one pint of low-strength beer/lager/cider (3.6% ABV) equals 2 units, a standard (175 ml) glass of wine (12% ABV) equals 2.1 units, and a single small (25 ml) shot of spirits (40% ABV) equals 1 unit.

References

AlphaBiolabs. Evans G. CDT blood testing. Last reviewed 22 Jan 2025. Available from: https://www.alphabiolabs.co.uk/learning-centre/cdt-blood-testing/. Accessed 06 Apr 2026.

Bortolotti F, Sorio D, Bertaso A, et al. Analytical and diagnostic aspects of carbohydrate deficient transferrin (CDT): A critical review over years 2007-2017. J Pharm Biomed Anal. 2018;147:2-12. doi: 10.1016/j.jpba.2017.09.006. Available from: https://pubmed.ncbi.nlm.nih.gov/28912047/.

Drinkaware. UK low risk drinking guidelines. Available from: https://www.drinkaware.co.uk/facts/information-about-alcohol/alcohol-and-the-facts/low-risk-drinking-guidelines#uklowriskdrinkingguidelines. Accessed 06 Apr 2026.

Fleming MF, Anton RF, Spies CD. A review of genetic, biological, pharmacological, and clinical factors that affect carbohydrate-deficient transferrin levels. Alcohol Clin Exp Res. 2004;28(9):1347-55. doi: 10.1097/01.alc.0000139815.89794.be. Available from: https://pubmed.ncbi.nlm.nih.gov/15365305/.

NHS. Alcohol units. Available from: https://www.nhs.uk/live-well/alcohol-advice/calculating-alcohol-units/. Accessed 06 Apr 2026.

Sheffield Laboratory Medicine. Sheffield Teaching Hospitals NHS Foundation Trust. Carbohydrate Deficient Transferrin (CDT). Available from: https://sheffieldlaboratorymedicine.nhs.uk/search-test.php?search=3012. Accessed 06 Apr 2026.

Synnovis. Carbohydrate Deficient Transferrin: A Marker of Chronic Excessive Alcohol Consumption. 16 Dec 2016. https://www.synnovis.co.uk/news-and-press/carbohydrate-deficient-transferrin-a-marker-of-chronic-excessive-alcohol-consumption. Accessed 06 Apr 2026.

Walk-In-Clinic. CDR blood test. Available from: https://walkin-clinic.co.uk/blood-tests/carbohydrate-deficient-transferrin. Accessed 06 Apr 2026.