Elevations in mean red blood cell volume (MCV), serum gamma glutamyl transferase (GGT) and carbohydrate deficient transferrin (CDT) are markers of heavy drinking in preceding weeks. The difficulty in assessing their accuracy as diagnostic tests has been that self reported consumption is used as the gold standard but sometimes a biological marker may be more accurate than a self False positive results occur with GGT and MCV due to other causes of elevation. False positive MCV can occur as a result of vitamin B12 deficiency, folic acid deficiency, thyroid disease or chronic liver disease. False positives with GGT are due to other causes of liver disease.
