Healthy range for serum ALT and the clinical significance of "unhealthy" normal ALT levels in the Korean population

Background and Aims: It remains unclear whether the currently-used normal range for serum alanine aminotransferase (ALT) levels really reflects a healthy liver. The present study was conducted to evaluate the healthy range of serum ALT in the Korean adult population and to determine the clinical significance of unhealthy levels. Methods: We reviewed the medical records, including questionnaires and the results of laboratory and radiological tests conducted at the Health Promotion Center at Korea University Anam Hospital between March 2005 and February 2007. The records, written in questionnaire form, included baseline data, such as physical status, social behaviors, medication history, and past and present disease histories. Results: The mean age of the 7403 enrolled patients was 48years, and 49.9% of these patients were male. A healthy cohort was selected after excluding patients who showed any abnormalities of the factors that were significantly associated with the serum ALT level upon multivariate regression analysis. The upper limit of the healthy range of the serum ALT level (i.e. 95th percentile) in the healthy population was 31IU/L for males and 23IU/L for females. The prevalence of metabolic syndrome and insulin resistance (IR) were significantly higher in patients with an 'unhealthy' normal ALT level than in those with a healthy ALT level. Conclusion: In our study, the upper limit of the healthy range of the serum ALT level was 31IU/L for males and 23IU/L for females. An unhealthy normal ALT level was associated with a higher prevalence of metabolic syndrome and IR.