GPT and metabolic syndrome: The activity of ALT in the hepatocytes is 7000 fold greater than in the serum,17 and this abundance is the reason for using it as a marker for NAFLD in many epidemiological studies.18 Clark et al. proposed that elevated AST or ALT levels are predictive of the presence of NAFLD if two basic criteria are met: 1) exclusion of alternative chronic liver diseases, e.g. alcoholic liver disease, hepatitis B or C infection, and hemochromatosis; and 2) presence of features of the metabolic syndrome.