Measurement of carbohydrate-deficient transferrin (CDT) in a general medical clinic: Is this test useful in assessing alcohol consumption?

The aim of this study was to measure serum carbohydrate-deficient transferrin (CDT) in consecutive patients attending a general medical clinic with a range of alcohol intakes to determine its value in assessing such intake. Eighty-one consecutive patients (42 male, 39 female) aged 20-85 years (median = 49.5 years) attending an out-patient clinic were selected for the study. Each patient completed an alcohol diary detailing the units of alcohol consumed in the previous week, a CAGE questionnaire and an alcohol history, and underwent conventional blood tests including mean corpuscular volume (MCV), liver function tests, and gamma-glutamyl transferase (GGT). CDT was estimated using an enzyme immunoassay (CDTect, Pharmacia). The group comprised of 17 teetotallers, 28 light (<100 g/week): 23 moderate (100-400 g/week), and 13 heavy (>400 g/week) drinkers. Median serum CDT for heavy drinkers (25.5 U/l) was significantly higher than for the rest (median = 17 U/l, Kruskal-Wallis test, P = 0.01). Serum CDT correlated significantly with the CAGE score (Mann-Whitney test, P= 0.01), but poorly with alcohol diary records (I = 0.1, P = 0.4). However the correlations between GGT and diary records (r = 0.43. P = 0.001) and MCV with diary records (r = 0.5, P < 0.001) were significant. Sensitivity, specificity, and positive predictive value for elevated serun CDT were 69. 81 and 41% respectively in detecting heavy drinking. The positive predictive values for the various parameters were 43% for elevated serum GGT, 41% for raised erythrocyte MCV, and 75% for a positive score on the CAGE questionnaire. When a combination of the markers CDT, GGT, and MCV was used, elevation in two of the three markers detected heavy drinking with sensitivity of 85%, specificity of 88%, and positive predictive value of 61%. We conclude that, in out-patients with a wide range of alcohol intakes conventional markers such as serum GGT and erythrocyte MCV were more suitable than serum CDT for assessing alcohol intake. Serum CDT when used in combination with serum GGT and erythrocyte MCV was useful in detecting heavy drinking. The importance of careful history-taking including a standardized questionnaire is emphasized.