CDT measured by capillary electrophoresis.
Transferrin produced in the liver is post-translationally modified with the addition of a number of sialic acid side-chains. This process is controlled by two groups of enzymes, glucuronyl transferases which add the side-chains and sialidase which removes them. In a normal individual the majority of transferrin in the circulation has between three and five sialic acid groups. It was found that in subjects abusing alcohol there is a significant increase in the proportion of transferrin with fewer sialic acid side-chains. Carbohydrate deficient transferrin (CDT) is considered to be the group of transferrins having no side-chains (asialo), one (mono-sialo) and two (di-sialo). In normal subjects CDT comprises less than 1.6% of the total transferrin concentration. Excess alcohol intake significantly increases this percentage and the increase is independent of the presence of liver disease; alcohol appearing to affect the above mentioned enzyme systems directly. Drugs that induce GGT (e.g. anti-convulsants etc.) have no effect on CDT and it can, therefore, be used in the presence of such drugs. The relationship between %CDT and units of alcohol consumed is good, although less strong in pre-menopausal women than in men or post-menopausal women. Rare diseases of glycosylation (CDG syndromes) and the D variant of transferrin found in a small percentage of African subjects could theoretically cause false positive results.