Drivers with a driver’s license suspension for having driven under the influence of alcohol will have to perform a CDT (deficient carboxy transferrin) dosage satisfactory for their license to be returned to them.

The transferrine

Transferrin is a glycoprotein that helps transport iron in the body. This molecule carries at the end of its polypeptide chains not less than 4 sialic acid residues. In humans, transferrin exists in different forms depending on the number of sialic residues carried.

CDT training

Repeated alcohol consumption alters the sialylation of transferrin, resulting in the formation of weakly sialylated transferrin molecules.

Beyond a consumption of 50 grams of alcohol daily, sialylation is totally inhibited, we only find transferrin molecules with 1 sialylated group or none: these are the molecules of CDT or transferrin deficient in carbohydrate.

These new forms of transferrin have a half-life of 2 weeks, meaning that half of them will be gone after 2 weeks.

The dosage of CDT thus constitutes a specific marker of excessive and regular alcohol consumption.

Chronic and excessive alcohol consumption must be able to be scientifically proven without any possible ambiguity.

Of all the existing biomarkers, the CDT assay appears to be the most appropriate in the context of medical examinations for fitness to drive following a driver’s license suspension or cancellation, as it is both highly specific for chronic and very sensitive alcoholism.

There are, however, other biological markers that can be used to detect cases of masked consumption or alcohol dependence.

Two other markers of alcoholism

• The level of GammaGT (Gamma Glutamyl Transferase or Gamma Glutamyl Transpeptidase): it is used to assess hepatic activity. Its level increases with chronic alcohol consumption in a person with a healthy liver, and returns to normal after two months of abstinence. But the GammaGTs also increase in the case of viral hepatitis, cirrhosis of the liver, obesity, acute pancreatitis or with certain drugs;
• VGM (average globular volume): it allows to appreciate the volume of red blood cells. Two months of chronic alcohol consumption induces an increase in MVV, which returns to normal after 3 months of abstinence. But a vitamin B12 deficiency, digestive malabsorption, hypothyroidism, taking antivitamin K or smoking also increase MCV.

Sensitivity and specificity of markers

GammaGT and VGM are markers that appear to be both non-specific for chronic excessive alcoholism and insensitive.

In contrast, CDT, which is the unsialilated form of transferrin, is typical of excessive and repeated alcoholism:

• The CDT dosage is 97% specific: 97% of people who do not consume alcohol excessively and regularly have a normal CDT level. The CDT level is positive after a daily alcohol consumption of 50 to 80 grams per day;
• The CDT assay has a sensitivity of 82%: 82% of people who drink alcohol on a regular basis and abuse have an increased level of CDT;
• Excessive but occasional consumption of alcohol does not influence the level of CDT;
• A high CDT level returns to normal after 2 to 4 weeks of abstinence.

La prescription

The prescription for a dosage of CDT is made by an alcohol specialist or by the medical commission for the return of driving licenses. When a motorist is stopped while intoxicated, a blood test for a CDT assay may be taken.

Sampling

Venous blood puncture is carried out in a red Vacutainer® tube containing silica microparticles which activate coagulation and promote the separation of serum from other blood constituents.

The tube is transported at room temperature and then stored at 4 ° C. The analysis is carried out in one of the 180 laboratories authorized to perform it in France.

It is fully covered by Health Insurance.

The method of analysis

The results vary from one to two depending on the analysis method used. The International Federation of Biochemistry has proposed a standardization protocol for a standardized CDT, but only 10% of laboratories have adopted it to date.

The normal rate

The result gives the percentage of CDT relative to transferrin.

• CDT rate
• CDT rate> = 1,7% corresponds to a positive result.

After 2 weeks of abstinence corresponding to the half-life of CDT, the positive level returns to normal.

• In Switzerland, the technique used is different and the limit rate is raised to 2,5%.

False negatives

• To rule out false negative cases, international studies tend to lower the threshold to 1,3%.

False positives

Rare cases of false positives can be detected:

• genetic abnormalities of transferrin;
• severe liver failure;
• CDG syndrome (Carbohydrate Deficient Glycoprotein syndrome).

The reliability of the result

Unlike other methods used to detect markers of alcoholism which have the major drawback of being sensitive to many other factors, the CDT dosage is not influenced by:

• acute alcoholism;
• overweight;
• diabetes ;
• smoking;
• daily alcohol consumption
• drugs, especially those prescribed for withdrawal.

Drink from time to time, yes! But all the time, no!