Observational studies usually show some measures of liver function, such as ALT, ALP and GGT, associated with higher risk of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM). Among these liver enzymes, GGT is most strongly positively associated with both CVD and T2D, although GGT is a non-specific marker of liver function. ALT is more clearly positively associated with T2D than with CVD while the role of ALP is unclear.
Recent 2017 study on hepatic Involvement in Nepalese Subjects with Type 2 Diabetes Mellitus observed marginal, yet statistically significant increase of serum ALT (26.6±0.84 (diabetic) vs 20.0±0.69 (control), p=0.003) and GGT (40.4±1.51(diabetic) vs 21.2±1.1(control), p<0.001) in the diabetic patients compared to healthy controls. Because of marginal elevation of liver enzymes within normal range in diabetic patients, estimation of liver enzymes is highly recommended for patients with T2DM for early detection of liver dysfunctions.
Both ALT and GGT have been shown in cross sectional studies to be modestly associated with the presence of fatty liver, whereas AST is not related. Significant elevation of ALT but not AST may be due to the reason that ALT is more specific serum liver marker. The usual observed biochemical pattern in hepatic steatosis due to NAFLD is of increased levels of transaminases, with alanine aminotransferase (ALT) levels exceeding those of aspartate aminotransferase (AST). Hepatic steatosis due to alcohol excess is often associated with an AST:ALT ratio >1.5, unlike non-alcoholic fatty liver disease.