Serum Alanine Aminotransferase Trends and Their Relationship with Obesity and Metabolic Syndrome in United States Adolescents, 1999-2014

Introduction: Nonalcoholic fatty liver disease (NAFLD), characterized by hepatocyte dysfunction, fat accumulation, and fibrosis, is the most common cause of chronic liver disease in children. Elevated levels of serum alanine aminotransferase (ALT) are used clinically to identify potential liver dysfunction. Our goal was to assess for changes in the national prevalence of elevated ALT over time and potential relationship to trends in the metabolic syndrome (MetS) severity and elevated body mass index (BMI). Materials and Methods: We studied 5411 non-Hispanic white, non-Hispanic black, and Hispanic adolescents aged 12-19 with complete MetS Z-score and ALT data from the National Health and Nutrition Examination Survey 1999-2014. Elevated ALT levels were defined by two different cutoffs: one for both sexes (30 U/L) and another that was sex specific (22 U/L girls; 25 U/L boys). MetS severity was assessed using a sex-and race-/ ethnicity-specific MetS Z-score. Results: We did not find a statistically significant linear increase in either mean ALT or the prevalence of elevated ALT differed over time. As expected, ALT levels were significantly correlated with BMI Z-score and MetS Z-score (P < 0.0001). Over time, BMI Z-scores increased and MetS severity Z-score decreased. Conclusion: Prevalence of elevated ALT did not exhibit a linear change between 1999 and 2014 in U.S. adolescents, potentially due to divergent trends regarding BMI and MetS severity. Continued vigilance in monitoring BMI and ALT levels is advised for the U.S. adolescent population. MetS Z-score could act as an additional tool to monitor risk of elevated ALT and subsequent development of NAFLD.