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Laboratory markers carbohydrate-deficient transferrin, gamma-glutamyltransferase, and mean corpuscular volume are not useful as screening tools for high-risk drinking in the general population: results from the Study of Health in Pomerania (SHIP).

BACKGROUND
Assessment of high-risk drinking in the general population can be problematic: questionnaire-based instruments may carry the problem of random or systematic recall bias, and the effectiveness of screening of single biomarkers has been shown to be insufficient. In this article, we analyze the alcohol intake/biomarker relationship of carbohydrate-deficient transferrin (CDT), gamma-glutamyltransferase (GGT), and erythrocyte mean corpuscular volume (MCV). Specific aims were (1) screening effectiveness comparison of GGT, CDT, and MCV in terms of sensitivity, specificity, and positive (PPVs) and negative predictive values (NPVs) and the effect of covariates on these measures; (2) the comparison of summary measures for the effectiveness of screening: the receiver characteristic curve (ROC) and the area under the ROC; and (3) to answer the question of which covariates effect which biomarkers and whether accounting for relevant covariates increases the prognostic value of biomarkers to levels that allow for application in the general population.


METHODS
In a representative cross-sectional health survey in northeast Germany with data collection from 1997 to 2001, 4310 men and women were asked for their recent alcohol consumption and smoking. Biomarkers were analyzed from blood samples. The effectiveness of screening of CDT, GGT, and MCV for high-risk drinking (men: >60 g/day, women: >40 g/day) was analyzed with PPV and ROC curve analysis.


RESULTS
For all three biomarkers, PPVs for high-risk drinking are very low (< 50%). There are some effects of covariates on screening effectiveness and on PPV, and knowledge of these covariates increases screening effectiveness, but no subgroup that had a combination of covariate levels and prevalence of high-risk drinking that led to a PPV > 50% could be found.


CONCLUSIONS
: Accounting for covariates in the screening procedure does not lead to a sufficient increase in PPV. Screening effectiveness of laboratory markers CDT, GGT, and MCV is insufficient for their application as screening tools for high-risk alcohol drinking in the general population. This was found using self-reported alcohol consumption as an imperfect gold standard, which is a limitation of the study, although self-reports are the standard instrument in comparable epidemiologic studies.