People who request the confirmation or reinstatement of their driving licence, which has been challenged or revoked because of alcohol intoxication, are subjected to tests to assess their alcohol consumption.
Tests concerning alcohol consumption may also be carried out to assess fitness for work duties.
These procedures should, and in part do, have a behavioral rather than toxicological meaning: in other words, they aim to establish whether a person is able to remain abstinent from alcohol, or at least to avoid drinking regularly and heavily, knowing that they will have to undergo an alcohol-related assessment. The assumption is that if a person is unable to refrain from drinking for the required period, they may have an uncontrolled relationship with alcohol, or may behave carelessly enough to suggest that they would not be sufficiently attentive to avoiding alcohol before driving.
In practice, however, tests with limited specificity may sometimes be used, that is, tests that can be altered by a number of conditions unrelated to alcohol consumption.
Those who develop tests to identify alcohol consumers are concerned with two parameters: whether the test can identify the greatest possible number of consumers (sensitivity) and whether the test avoids incorrectly classifying people who do not consume alcohol as consumers (specificity).
From the point of view of someone who needs to defend their right to drive or work, it is important to avoid being unfairly classified as “positive.”
With this in mind, some considerations concerning the main tests used to identify alcohol consumption are useful.
CDT (Carbohydrate-Deficient Transferrin)
CDT is currently considered the most reliable single test and is capable of identifying sustained and fairly substantial alcohol consumption during the previous 15 days. In other words, a positive result indicates that a person has consumed a significant amount of alcohol, either continuously or repeatedly, during the preceding 15 days.
Its specificity is approximately 95% when capillary electrophoresis or high-performance liquid chromatography (HPLC) methods are used. This nevertheless means that, statistically, it may incorrectly indicate alcohol consumption in about 5 out of 100 cases.
Depending on the specific technique used, the ability to identify causes of false-positive results, such as genetic variants, may differ. The result is expressed as the percentage of CDT relative to total transferrin.
The best way to ensure reliable results is to use two tests on the same sample. The first test (screening) is performed using a technique with a high ability to identify all potentially positive cases, including some false positives. If the result is positive, a confirmatory test is then performed, with greater ability to distinguish true positive cases from errors.
Confirmatory tests are not generally used as the initial test because, although they are more precise, they may fail to identify some cases of alcohol consumption that should otherwise be classified as positive. In other words, the screening test conducts a “raid” that may include some innocent people, while the confirmatory test releases those who were wrongly included.
Gamma-GT
Gamma-GT is a parameter originating primarily from the liver, but it is not specific to alcohol consumption because it can increase for many other reasons.
Among the most common are overweight, various medications that stimulate its activity (for example, antiepileptic drugs), diabetes, myocardial infarction, various types of trauma, pancreatitis, kidney disease and hyperthyroidism.
Gamma-GT alone should therefore not be considered an acceptable parameter for classifying someone as an alcohol consumer.
Mean Corpuscular Volume (MCV)
MCV measures the average volume of red blood cells. It has low specificity and is not always increased in people who consume alcohol.
It should therefore not be used alone to identify alcohol consumption.
Transaminases (ALT/GPT and AST/GOT)
These are enzymes found in the liver, but not exclusively there. An AST/ALT ratio greater than 2 may be suggestive of alcohol-related liver damage, but these parameters are not specific because they may also increase as a result of muscle injury or myocardial infarction.
Furthermore, they do not increase in every person who consumes alcohol, nor do they increase proportionally to the amount of alcohol consumed.
CDT and Gamma-GT together (Gamma-CDT)
It is possible to calculate a combined index using CDT and Gamma-GT values. This can increase the accuracy with which moderate but regular alcohol consumption during the preceding 2–3 weeks is identified.
There are also other parameters that are particularly useful for determining whether a state of intoxication is attributable to an isolated, occasional episode or to continued consumption.
Alcohol can be measured directly in the blood and, if positive, this would naturally be the clearest parameter for identifying problematic drinking in someone who was expected to remain abstinent. It indicates alcohol consumption immediately preceding the blood sample and may suggest that the person is unable to control when and how much they drink, or that they drink continuously and therefore also drank shortly before the test.
Ethyl Glucuronide and Ethyl Sulfate
Depending on the amount consumed, ethyl glucuronide (EtG) and ethyl sulfate (EtS) can be detected in urine for varying periods, approximately 6 to 100 hours after consumption.
Thus, even when alcohol is no longer detectable in the blood, recent alcohol consumption may still be identified, in some circumstances up to approximately four days earlier, depending on the amount consumed and the testing method.
Fatty Acid Ethyl Esters (FAEE)
FAEEs may be present in the blood for approximately 24 hours after an isolated episode of consumption, but may remain detectable for up to approximately 100 hours when alcohol consumption has been repeated recently.
Finally, there are circumstances in which it is necessary to establish the relationship between a person’s alcohol-related condition and an event that has already occurred, such as a traffic accident.
In such cases, it is important to know that the effects of alcohol, as reported in standard tables, are influenced by tolerance, that is, adaptation resulting from habitual consumption.
The same quantity of alcohol consumed in beverages can correspond to different blood alcohol levels depending on the person’s degree of adaptation (metabolic or kinetic tolerance).
Conversely, the same blood alcohol concentration can produce different effects depending on the degree of adaptation (dynamic tolerance).
Furthermore, the same alcohol-induced effect may correspond to different degrees of behavioral impairment depending on the circumstances in which it occurs, for example in a familiar or unfamiliar environment.
Conclusion
For people undergoing alcohol-related testing for driving-licence purposes, it is advisable to verify that reliable parameters are being used, preferably CDT or a validated combination such as Gamma-CDT, rather than relying solely on Gamma-GT, transaminases or MCV, whether individually or combined.
It is also useful to document one’s health conditions, including any medications being taken at the time of the blood sample.
It is important to establish whether the testing procedure includes both a screening test and a confirmatory test, and to know that, where such a procedure is used, the final assessment should be based on the confirmatory result rather than the screening result.
Furthermore, the context of an assessment can distinguish between the presence and extent of alcohol consumption—whether occasional or habitual—and the pattern of alcohol use, including whether it appears controlled or uncontrolled.
In the event of a dispute, these aspects should be reviewed and, where appropriate, supported through legal channels and/or with the assistance of a physician of one’s choice.
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