Aminotransferase Upper Reference Limits and the Prevalence of Elevated Aminotransferases in the Korean Adolescent Population

Objectives: For the pediatric population, upper reference limits (URLs) for aminotransferase levels have not been established. The prevalence of high aminotransferase levels provides important information regarding the burden of liver disease in the current childhood obesity endemic. Methods: We set the URL of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) for participants ages 10 to 19 years (n = 2746) from the 2007 to 2009 Korea National Health and Nutrition Examination Survey at the 97.5th percentile of that population who were determined to be at low risk for liver disease (n = 1717; low risk was defined as testing negative for hepatitis B virus surface antigens, the absence of alcohol use disorder, having normal body mass index, and having normal lipid or carbohydrate metabolism). Results: The URLs for ALT were 33 IU/L for boys and 25 IU/L for girls, and the corresponding limits for AST were 33 IU/L for boys and 28 IU/L for girls. The weighted prevalence of elevated ALT levels was 6.5% in the sample, 8.2% in boys and 4.5% in girls. The prevalence of elevated AST levels was 3.9% and had no sex differences. We also found that elevated ALT levels are associated with male sex, older age, obesity, and presence of abnormal lipid levels. Having elevated AST levels is associated with obesity, younger age, and exhibiting laboratory indicators of abnormal lipid metabolism. Conclusions: Aminotransferase URLs are being established for the first time, and our results may be useful in determining a baseline level for monitoring the secular trends of liver disease in future studies of adolescent populations.