An important focus of alcohol research is the search for biological markers that could be used in simple screening tests to identify people who are at risk for alcoholism or who already are chronic heavy drinkers. Two categories of biological markers exist: state markers, which reflect a person's alcohol consumption, and trait markers, which indicate a predisposition for alcoholism.
State markers fall into two main groups: screening markers and relapse markers. Screening markers, which detect chronic alcohol consumption, could complement information obtained from patients in the course of taking their medical history. This physical information could provide important diagnostic clues because, as clinical observations suggest, many people do not accurately report their level of alcohol consumption. Thus, screening markers could be useful in the early identification of alcoholism, especially in patients who consume alcohol in amounts that do not lead to acute medical problems but that could have longterm behavioral or medical consequences. In contrast, relapse markers, which are sensitive to acute alcohol consumption, could play an important role in monitoring recovering alcoholics and other heavy drinkers. State markers that would permit the identification of heavy drinkers even when alcohol is no longer present in the blood would be particularly valuable diagnostic tools.
Trait markers could help identify people at risk for alcoholism who could benefit most from early, targeted prevention and intervention approaches. These high-risk populations most prominently include first-degree relatives of alcoholics. Trait markers also could provide important research tools for evaluating the genetic and environmental factors that may predispose a person to alcoholism.
Chronic ingestion of large quantities of alcohol alters many physiological and biological processes and compounds, including several blood-related (i.e., hematological) variables. Because blood samples are relatively easy to obtain, structural and functional changes in circulating blood cells and plasma proteins potentially can form the basis of laboratory tests for screening, diagnosing, and monitoring alcoholism. Two hematological state markers commonly used for these purposes are the presence of carbohydrate-deficient transferrin (CDT) in the blood and an increase in the size of red blood cells (RBC's), as measured by the mean corpuscular volume (MCV).
Carbohydrate-Deficient Transferrin. CDT is one of the newest-and perhaps the most promising-of the hematological state markers. Transferrin is an iron-containing protein in the plasma that transports iron, which is stored at various sites in the body, to the developing RBC's in the bone marrow for incorporation into hemoglobin. Transferrin molecules in the blood usually contain several carbohydrate components. In chronic heavy drinkers, however, the number of carbohydrate components in each transferrin molecule is reduced, resulting in CDT. The mechanism underlying this alteration still is unclear.
Because elevated CDT levels in the blood appear to be a specific consequence of excessive alcohol consumption, a recent study investigated the utility of repeatedly monitoring serum CDT to detect relapse among recovering alcoholics. The study found that in most of the subjects who relapsed, the elevation of CDT levels preceded self-reported alcohol consumption by at least 28 days. These findings suggest that repeated testing of alcoholic patients for CDT permits early relapse detection and thus may lead to early intervention. Early intervention, in turn, may decrease the need to rehospitalize patients for alcohol withdrawal and prevent some of the complications associated with sustained excessive drinking.
Mean Corpuscular Volume. …