Several biochemical markers of alcohol abuse, both acute and chronic, have been proposed and can be measured in urine and/or blood. They represent a tool to assess the amount and mode (chronic or acute) of alcohol consumption, and the damage induced on the body by alcoholism. Biomarkers can be classified as direct, i.e., derived directly from the metabolism of ethanol, and indirect, which are released due to alterations induced by ethanol. The latter is characterized by low diagnostic sensitivity and specificity because it increases significantly only after high and regular intake of alcohol, and its levels may vary in response to factors unrelated to ethanol.

Alongside established biomarkers, such as aspartate aminotransferase, alanine aminotransferase, γ-glutamyltransferase, and mean corpuscular volume of erythrocytes, which are positive only in advanced states of alcohol-related dis eases, new, earlier, and more specific markers have been identified (Table 1), the main ones of which are (Fig. 1):

Table1. Biomarkers of alcohol use

Fig1. Detection times of the biomarkers of alcoholism. (Copyright EDISES 2021. Reproduced with permission)

• Blood ethanol (EtOH)

 • Urinary ethanol (EtOH)

 • EtG (ethylglucuronide)

• CDT (carbohydrate transferrin)

Blood Ethanol

Circulating ethanol levels are a direct and reliable marker of recent alcohol intake. In addition, assessment of blood ethanol values can give insight into long-term ethanol consumption patterns (Table 2).

Table2. Interpretation of blood ethanol concentration

Ethanol has a short half-life, about 30 minutes, and there fore, its presence can only be detected for a short period.

 Urinary Ethanol

Ethanol peaks in the urine 45–60 minutes after ingestion. Ethanol levels in the urine are generally higher than the corresponding blood levels; this is true in the elimination phase, after ethanol has reached its peak in the blood and, therefore, its circulating levels begin to decline. In addition, alcohol in urine can be detected for a more extended period (up to 1–2 hours longer) than in blood because the urine remains in the bladder for a period. Urinary ethanol is characterized by marked interindividual fluctuations.

The presence of alcohol in the urine indicates recent previous intake but may not be related to the degree of intoxication observed at the time of sample collection. The level of ethanol in the sample refers only to the average concentration of alcohol in the blood during the time it takes for the urine sample to accumulate in the bladder, not to the concentration of alcohol in the blood at the time of collection.

False-negative results may be caused by the volatility of the alcohol. Urine alcohol concentrations may decrease by 10–25% during each hour before the urine sample is analyzed.

Ethylglucuronide (EtD)

Ethylglucuronide is a direct minor metabolite of ethanol and is considered highly specific for the assessment of recent alcohol intake. In particular, it is an ethanol conjugation product formed by reaction with activated glucuronic acid (uridin-5′-diphospho-β-glucuronic acid [UDPGA]) mediated by the uridine-diphosphate glucuronosyltransferase (UGT) enzyme.

EtG is in various biological fluids, tissues, and hair. However, it is generally measured in urine. EtG can remain positive for several days after the discontinuation of ethanol intake and, therefore, may provide added value in assessing recent alcohol consumption. In particular, in urine remains for 40–60 hours after alcoholic intake. In the blood, instead, it is detectable up to 14 hours after the intake; an occasional intake of alcohol is enough to exceed the threshold of 0.5 mg/L.

Some studies have indicated diagnostic applications of EtG in postmortem assessments of alcohol consumption and fetal alcohol exposure or in patients awaiting liver transplantation.

Polymorphic variants in genes encoding UGT may have a significant impact on the ability of humans to synthesize EtG and may, therefore, explain interindividual differences in EtG levels after alcohol consumption.

Carbohydrate Transferrin (CDT)

Carbohydrate transferrin is a specific marker of chronic alcohol abuse.

Transferrin is a serum protein that transports iron in the circulation to the target organs (bone marrow, liver, and spleen). From a structural point of view, transferrin is a glycoprotein consisting of a polypeptide with two polysaccharide chains linked with sialic acid residues. The addition of sialic acid occurs through a posttranslational reaction mediated by an enzymatic system with ethanol-dependent glucosyltransferase activity; ethanol and its metabolite, acetaldehyde, reduce the enzymatic activity of this system.

There are several forms of transferrin, which differ in the number of iron atoms carried (0–2), the primary structure (genetically determined), and the number of sialic acid resi dues (0–8). Most circulating transferrin (>80%) contains four sialic acid residues (tetrasialotransferrin, TeST); the form with two residues (disialotransferrin, DST) is physio logically present in amounts <2 %, while the desialylated form (asialotransferrin, aST) is almost absent. In the case of massive and continuous ethanol intake, the desialylated fraction increases. The term CDT refers to the set of low sialic acid transferrins and, particularly to the aST and DST forms. CDT has a longer half-life (10 days) than transferrin in the circulation (7 days).

CDT elevation requires the consumption of at least 50–80 g of ethanol per day for several weeks and, therefore, has low sensitivity when used as a screening tool in the gen eral population. However, in alcohol-dependent patients, it is sufficiently sensitive to detect relapse and monitor sobriety.