Transferrin is synthesized primarily by hepatocytes and functions as an iron-transporting glycoprotein with two iron-binding sites. Transferrin exists in multiple isoforms classified by the number of terminal sialic acid residues. In healthy individuals, transferrin predominantly contains 4 sialic acid residues. Tetrasialotransferrin accounts for approximately 75–80% of total plasma transferrin. Other isoforms such as hexasialo, pentasialo, trisialo, and disialotransferrin are present in much smaller proportions.
Chronic alcohol consumption disrupts sialylation, leading to increased quantities of disialo- and asialotransferrin. Sustained intake of 50–80 grams of ethanol per day over 1–2 weeks results in loss of carbohydrate side chains and elevated CDT levels. Elevated concentrations typically normalize during abstinence, with a half-life of approximately 10 to 15 days.
Carbohydrate deficient transferrin (CDT) is internationally accepted for detecting and monitoring excessive alcohol consumption due to its high specificity and lower false-positive rates compared to other biomarkers. Sensitivity for heavy drinking is 60-70% and specificity is 95%.
It is important to remember that congenital disorders of glycosylation can also produce CDT. However, alcohol consumption increases the relative amount of monosialyted transferrin more than is seen in congenital disorders of glycosylation. Other conditions such as hereditary fructose intolerance, galactosemia, and liver disease may result in increased levels of CDT. Bacterial contamination of the specimen may also cause falsely elevated CDT values.
CDT testing alone is not recommended for general screening for alcoholism. CDT testing should be combined with gamma glutamyltransferase, mean corpuscular volume, and ethylglucuronide analysis. Together, these tests can identify the majority of patients who consume a large amount of alcohol.
Transferrin is separated by capillary electrophoresis and the relative quantity of CDT is determined. Normal level of CDT is 0-1.3%. Levels between 1.4% to 1.6% are inconclusive. A threshold of 1.7% or greater is indicative of chronic and excessive alcohol consumption.
Specimen requirement is a red top tube of blood.
References
Golka K, Wiese A. Carbohydrate-deficient transferrin (CDT)--a biomarker for long-term alcohol consumption. J Toxicol Environ Health B Crit Rev. 2004 Jul-Aug;7(4):319-37. doi: 10.1080/10937400490432400
Chrostek L, Cylwik B, Szmitkowski M, Korcz W. The diagnostic accuracy of carbohydrate-deficient transferrin, sialic acid and commonly used markers of alcohol abuse during abstinence. Clin Chim Acta. 2006;364((1-2)):167–71. doi: 10.1016/j.cccn.2005.06.020.
Fagan, K.J., Irvine, K.M., McWhinney, B.C. et al. Diagnostic sensitivity of carbohydrate deficient transferrin in heavy drinkers. BMC Gastroenterol 14, 97 (2014). https://doi.org/10.1186/1471-230X-14-97
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