The CDT (Carbohydrate Deficient Transferrin) rate is the biological marker on which the decision to restore a driving license after an alcohol-related offense is based. The difficulty for the affected drivers lies less in the measurement itself than in the interpretation of the result: the threshold varies according to laboratories and medical commissions, creating situations where the same number leads to two opposing decisions.
CDT thresholds set in 2025: comparative table of laboratories and commissions
The first reflex after a blood test is to compare the obtained value with the norm indicated on the report. The problem is that this norm is not uniform.
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| Source of the threshold | Reference value CDT | Practical interpretation |
|---|---|---|
| Majority of prefectural medical commissions | 1.7% maximum | Above this, frequent refusal to restore the license |
| Some laboratories (internal biological standard) | 2.0% | The result may appear “normal” on the report while exceeding the commission’s threshold |
| Gray area identified by laboratory networks (Cerballiance, Eurofins) | Between 1.7% and 2.0% | Case-by-case interpretation, often unfavorable before the commission |
Since 2023-2024, several major laboratory groups have standardized their reports by distinguishing a “non-excessive drinker” reference value (around 1.7%) and this gray area. Before this standardization, only the raw number and the laboratory’s internal standard were included in the results, which maintained confusion.
A driver with a CDT rate of 1.8% may therefore receive a report mentioning a “normal” result according to the laboratory, while being denied the restoration of their license by the medical commission. To calculate their CDT rate for the license and anticipate the decision, one must refer to the threshold of 1.7% and not to the standard printed on the analysis sheet.
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CDT, Gamma GT, and MCV: what the medical commission actually cross-references
The CDT rate is not examined in isolation. The medical commission for the driving license systematically requests three blood markers related to alcohol consumption.
- CDT (desialylated transferrin): marker of excessive and regular alcohol consumption over the two to four weeks preceding the sample. The most specific of the three for detecting chronic alcohol use.
- Gamma GT (gamma-glutamyltransferase): liver enzyme that increases with regular consumption, but also due to liver pathologies, certain medications, or overweight. Less specific than CDT.
- MCV (mean corpuscular volume): measures the size of red blood cells. A high MCV can indicate chronic alcohol consumption, but also a deficiency in vitamins B9 or B12.
In practice, a CDT of 1.7% or lower accompanied by Gamma GT and MCV within the norms generally leads to a favorable opinion. Conversely, a CDT slightly above the threshold with high Gamma GT almost systematically triggers a refusal or a request for additional testing.
The emergence of EtG testing as a complement
Since 2023, an emerging practice is modifying the evaluation in borderline cases. Several medical commissions and approved doctors are requesting a complementary test for ethyl glucuronide (EtG), either urinary or hair, when the CDT is in the gray area (between 1.7% and 2.0%).
Hair EtG testing can detect alcohol consumption over a period of up to several months, whereas CDT only covers two to four weeks. This testing is not yet systematic in regulatory texts, but it carries weight in the final decision when the classic biological file leaves room for doubt.
Normalization period for CDT rate after stopping alcohol
The half-life of CDT is around two weeks. After complete cessation of alcohol consumption, the CDT rate begins to decrease and can return below the threshold of 1.7% in two to four weeks of total abstinence.
This data should be nuanced. The speed of normalization depends on the level of prior consumption, the duration of that consumption, and individual metabolism. A daily drinker for several years will not return to the same rate as an occasional consumer in the same timeframe.
Common mistake regarding the timing of the blood test
Many drivers have their blood test done too early in relation to their cessation date or too late in relation to the date of the medical commission (the result must be recent). The test should be performed long enough after stopping for the rate to have decreased, but close enough to the medical visit for the result to be considered representative.
A result above 1.7% during the first medical visit does not definitively close the door. The commission may grant a delay and request a second biological check at a later date, usually after a few months, to verify the evolution of the rate.
Medical visit for the license after suspension: process and pitfalls to know
The medical visit is mandatory after a suspension, judicial cancellation, or administrative invalidation of the driving license related to alcohol. It takes place either before a doctor approved by the prefecture or before the prefectural medical commission depending on the department and the type of offense.
The driver must present their blood test results (CDT, Gamma GT, MCV), proof of identity, and the summons letter or suspension decision. The doctor or commission issues a fitness, unfitness, or temporary fitness opinion with restrictions.
The most common pitfall concerns drivers whose CDT rate is below 2% but above 1.7%. The laboratory report shows “normal,” the driver presents confidently, and the commission refuses restoration by applying the stricter threshold. Checking the threshold retained by their commission before the visit helps avoid this situation and, if necessary, reschedule the blood test after an additional period of abstinence.
The distinction between these thresholds remains the main friction point in the procedures for recovering the license in 2025. Knowing the exact value retained by the commission in their department, and not that of the laboratory, conditions the success of the process.