BMI Metrics Are Poor Predictors of Pediatric Nonalcoholic Fatty Liver Disease Severity

Abstract

Background: Alternative BMI metrics are superior to BMI z score (BMIz) in tracking obesity but have not been evaluated in patients with nonalcoholic fatty liver disease (NAFLD). Our objective was to evaluate whether BMI-adjusted z score (BMIaz) or BMI expressed as a percentage of the 95th percentile (%BMIp95) are better predictors of degree of alanine aminotransferase (ALT) elevation, a surrogate for NAFLD severity, compared with BMIz in patients with NAFLD. Methods: A retrospective study of 776 subjects aged 2-18 years with BMIz > 1.0 followed in a NAFLD subspecialty clinic was conducted. Regression analysis was used to determine predictors of elevated ALT. Results: There was no association between BMIz, BMIaz, or %BMIp95 and degree of ALT elevation using linear or logistic regression. Conclusion: These results do not support the use of alternative BMI metrics for evaluating NAFLD severity. Future studies should investigate longitudinal assessments and correlation with histology.

Keywords: BMI; BMI z score; NAFLD; NASH; obesity.

Figure 1.

Scatter plots of each BMI metric (BMIz, BMIaz, and %BMIp95) and log-transformed ALT level in the entire cohort (A–C) and in the subgroup of subjects <10 years (D–F). %BMIp95, BMI expressed as a percentage of the 95th percentile; ALT, alanine aminotransferase; BMIaz, BMI-adjusted z score; BMIz, BMI z score.