BACKGROUND: Screening medical patients for excessive alcohol drinking is important because minimal intervention by physicians is effective in reducing excessive consumption. Screening tests, such as biologic markers of alcohol consumption, should therefore be investigated to assess their validity to detect alcohol drinking. METHOD: Levels of carbohydrate-deficient transferrin (CDT), gamma-glutamyltransferase (GGT), and mean corpuscular volume (MCV) were determined in 1202 consecutive patients (20 to 75 years old) seen at the medical emergency ward (n = 552) and the primary care center (n = 650) of a city and teaching hospital. Each eligible patient was administered a CAGE questionnaire (an acronym for questions regarding cutting down on drinking, annoyance at others' concern about drinking, feeling guilty about drinking, and using alcohol as an eye-opener in the morning), and for each CAGE-positive patient (score > or = 2) as well as for a random sex-matched sample of CAGE-negative patients, standardized data about the recent level of alcohol drinking, morbidities, drug therapy, and smoking were recorded. The operating characteristics of CDT, GGT, and MCV were determined according to alcohol consumption and the CAGE test. Sensitivities, specificities, and receiver operating characteristic curves were computed to compare the tests at different cutoff values. RESULTS: Levels of CDT were elevated in 21% of men and 7% of women. According to recent alcohol consumption in men (> 60 g/d), the respective sensitivity and specificity of the tests were 0.58 and 0.82 for CDT, 0.69 and 0.65 for GGT, and 0.27 and 0.91 for MCV. Overall, receiver operating characteristic curves demonstrated similar performance of the three tests for screening of excessive alcohol drinking or alcohol abuse. However, in young men (< 40 years of age) and in smokers, CDT was superior to GGT or MCV. CONCLUSIONS: The study suggests that CDT determination may be a useful test for screening programs of excessive alcohol drinking in young male medical patients.