Carbohydrate Deficient Transferrin (CDT)
Biochemistry Overview / Directory
Purpose of the test
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.
For more detailed information, please download the "CDT Info" file below.
Test PDF
Reference Range
CDT < or = 1.5% : No excess alcohol intake
CDT 1.6-1.9% : Intake may be high but not necessarily in the range of dependence
CDT > or = 2.0% : Excess alcohol intake
Sample Requirements
Serum (500 µL).
Storage and Transport
Stable at 4°C for up to one week. Send by overnight first class post.
Turnaround Time
The assay is run every week.
Price
Price available on application - please contact adrian.turner@kch.nhs.uk. Discounts could be available for significant workloads.
Contacts
Colin Stone
T 020 3299 4128 / 4121
