Carbohydrate deficient transferrin

Carbohydrate-deficient transferrin (CDT) is a laboratory test used to help detect heavy ethanol consumption.

Carbohydrate-deficient transferrin is elevated in the blood of heavy alcoholism but raised levels can also be found in a number of medical conditions.

Transferrin is a plasma protein that carries iron through the bloodstream to the bone marrow, where red blood cells are manufactured, as well as to the liver and spleen. Structurally, transferrin is a polypeptide with two N-linked polysaccharide chains. These polysaccharide chains are branched with sialic acid residues. Sialic acid is a monosaccharide carbohydrate.

Various forms of transferrin exist, with differing levels of sialylation. The most common form is tetrasialotransferrin, with four sialic acid chains. In persons who consume significant quantities of alcohol (usually more than 4 or 5 alcoholic beverages a day for two weeks or more), the proportion of transferrin with zero, one, or two sialic acid chains is increased. These are referred to as carbohydrate-deficient transferrins. These carbohydrate-deficient transferrins can be measured in the bloodstream, and are an important marker for alcohol abuse. Used with other tests, such as gamma glutamyl transferase (GGT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT), carbohydrate-deficient transferrin can be a useful tool in identifying problem drinking, such as alcohol abuse or alcoholism.

CDT is measured by taking a sample of a patient's blood. Apparently healthy individuals with no or low reported alcohol consumption and a negative Alcohol Use Disorder Identification Test will have a %CDT <3.0 (95th percentile for the social drinking population). Elevated levels of CDT suggest recent alcohol abuse, especially if other liver-associated enzymes (such as γGT) are elevated. Although recent heavy alcohol use is most commonly associated with elevated CDT, certain rare liver disorders can also increase levels of CDT.