Upper limit of normal serum alanine and aspartate aminotransferase levels in Korea

Background and Aim: The widely accepted range of upper limits of normal (ULN) alanine aminotransferase (ALT) levels (ULN < 40 U/L) was recently challenged by several reports. Both ALT and aspartate aminotransferase (AST) are commonly used as surrogate markers of liver disease, but almost all studies of aminotransferase activity were conducted on ALT. We investigated not only ULN of ALT but also AST activity and to identify factors modulating them in healthy Korean. Methods: A cross‐sectional study of 411 240 registered blood donors in all nationwide blood banks belonging to the Korean Red Cross were conducted. ULN of ALT and AST was evaluated adjusting their age according to the national population census database. “Decision tree model” was used to identify the affecting factors of ALT and AST and optimal cut‐off points of affecting factors. Results: “ULN of ALT” was 34 U/L in men and 24 U/L in women and “ULN of AST” was 32 U/L in men and 26 U/L in women in the blood donor database. Decision tree analysis showed that ALT levels were mostly influenced by body mass index level and its critical two cut‐off points were 23.5 kg/m² and 25.8 kg/m², respectively. The most affecting factor of AST was gender. Conclusion: Upper limits of normal of ALT and AST in Koreans were lower than conventional accepted values (< 40 U/L) but higher than recently suggested values (male < 30 U/L and female < 19 U/L). Body mass index was the most determining factor for ALT and gender was the most influencing factor for AST activity.