Diagnostic Use
Carbohydrate deficient transferrin can be used, in conjunction with other indicators, to assess a patient’s chronic alcohol consumption. It is not increased by a single episode of heavy alcohol consumption.
Interpretation
CDT is reported as a percentage of total transferrin, to reduce the effects of gender and varying transferrin concentrations.
95% of non-drinkers and individuals with normal drinking patterns will have CDT values below 1.7%. Values greater than 1.7% usually indicate a consumption of more than 60 g of ethanol per day over a period of at least one week. Note that 5% of individuals will therefore have a %CDT of >1.7% without excessive drinking. Therefore CDT values should be interpreted with caution.
In the case of complete abstinence in a patient with previously elevated concentrations, it can take up to two months for the %CDT to return to normal.
Although the %CDT is probably the most reliable indicator we have of alcohol consumption, it correlates poorly with the quantity of alcohol consumed. It also correlates poorly with other markers of alcohol consumption, and so these other markers (particularly GGT) also need to be considered when interpreting the result.
If both GGT and %CDT are normal, then there is probably no alcohol misuse.
If both are elevated, then there probably is misuse.
Other combinations (one normal, one abnormal) makes the result questionable.
False positive % CDT results may occur in patients with severe liver disease (any cause), autoimmune hepatitis, biliary cirrhosis, liver cell cancer, haemochromatosis, genetic transferrin variants and the rare CDG syndrome.
The most reliable interpretation is obtained with a series of %CDT tests to detect trends, with the tests being performed at 1 – 2 month intervals (to allow for the long half life of this protein – 15 days).
Test Method
Sebia capillary electrophoresis