The aim of this study was to identify the relationships between borderline serum liver enzyme abnormalities and the incidence of impaired fasting glucose (IFG) and diabetes mellitus (DM) during a 7-year follow-up of workers, and to evaluate the quantitative level of risks.

A total of 749 workers in an electronics manufacturing company were divided into the normal fasting blood glucose (n = 633), IFG (n = 98), and DM (n = 18) groups, according to the results of their health checkup in 2006. Among 633 workers in the normal group, excluding 55 workers who were impossible to follow, incidence rate and relative risks of 578 workers to the IFG or DM in 2013 according to the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (γ-GTP) were investigated. The liver enzyme levels were categorized as A (normal), B (borderline elevation), and R (definite elevation) following the standard of the National Health Insurance Service of Korea.

The incidence rate of IFG or DM based on ALT level was 9.7 % for the A, 30.0 % for B, and 15.4 % for R. According to γ-GTP, the incidence rate was 9.8 % for A, 34.5 % for B, and 25.0 % for R. The relative risk(RR) to the incidence of IFG or DM depending on the level of ALT were 3.09 in B and 1.59 in R compared to A. According to γ-GTP, RR was 3.52 in B and 2.55 in R compared to A. AST level was not related to the incidence of IFG or DM. A multiple logistic regression analysis with the incidence of IFG or DM as a dependent variable resulted in an odds ratio of 2.664(1.214–5.849) for B level ALT, 3.685(1.405–9.667) for B level of γ-GTP even after adjustment for other variables such as age, sex, body mass index, AUDIT score, systolic blood pressure, and triglyceride.

Even borderline elevations of ALT and γ-GTP, but not AST, increased the incidence and risk of IFG or DM after 7 years. Borderline elevation of ALT and γ-GTP was identified as an independent risk factor of IFG or DM.