Background: Non- alcoholic fatty liver disease (NAFLD) is a pathogenic factor of insulin resistance and type 2 diabetes. On the other hand, the circulating liver enzymes including Aspartate aminotransferase (AST), Alanin aminotranferase (ALT) and Gamma glutamyl transferase (GGT) are commonly elevated in asymptomatic patients with NAFLD.

Methods: As a nested case-control study, AST, ALT, GGT as well as classic diabetes risk factors, homeostatic model assessment of insulin resistance(HOMA- IR) and C-reactive protein (CRP) were measured in 133 non-diabetic subjects at baseline (68 cases and 65  controls). Conditional logistic regression was used to calculate the odds ratio (OR) of diabetes associated with different hepatic markers. We used factor analysis for clustering of classic diabetes risk factors.

Results: In Univariate analysis, both ALT and GGT were associated with diabetes with ORs of 3.07(1.21-7.79) and 2.91(1.29-6.53), respectively. After adjustment for CRP and insulin, ALT and GGT were still predictive of incident diabetes. When the model was further adjusted for anthropometric, blood pressure and metabolic factors resulted from factor analysis (full model), only ALT was independently associated with diabetes [OR=3.06 (1.01-9.26)]. No difference was found between the area under the receiver operating characteristic curves of the models with and without ALT (0.820 and 0.802 respectively, P=0.4)

Conclusion: ALT is associated with incident type 2 diabetes independent of classic risk factors. However, its addition to the classic risk factors does not improve the prediction of diabetes.