Can “Healthy” Normal Alanine Aminotransferase Levels Identify the Metabolically Obese Phenotype? Findings from The Korea National Health and Nutrition Examination Survey 2008–2010

Background There is no established parameter with which to screen metabolically obese phenotypes. Aim The aim of the study was to revise the upper limit of normal (ULN) of serum alanine aminotransferase (ALT) and to investigate the predictive value of updated ALT levels for metabolic obese phenotype stratified according to body mass index (BMI). Methods We analyzed a nationally representative data from the Fourth Korea National Health and Nutrition Examination Survey. This cross-sectional study included 2,416 healthy people aged 33.9 ± 0.3 years. The ULN of healthy ALT level was set at the 95th percentile of the healthy population. A metabolic obese phenotype was defined as having insulin resistance or metabolic syndrome. A logistic regression analysis was performed to assess the odds ratio for a metabolic obese phenotype according to the healthy ALT level. Results The revised ULN of serum ALT level in healthy participants were 30 IU/L and 22 IU/L for males and females, respectively. Serum ALT level was higher in individuals with metabolic obesity compared with those without metabolic obesity in both genders, stratified according to BMI. After adjusting for age, BMI, smoking, alcohol drinking, and regular physical activity, unhealthy normal ALT levels (males 30–40 IU/L, females 22–40 IU/L) were significantly associated with metabolic obesity, especially in both obese and non-obese women. Conclusions A newly revised threshold for ALT is proposed as a simple clinical metabolic parameter that can identify a metabolic obese phenotype. We suggest that people with unhealthy normal ALT levels may need further investigation for the presence of metabolic obesity.