Revision of serum ALT upper limits of normal facilitates assessment of mild liver injury in obese children with non-alcoholic fatty liver disease.

BACKGROUND: The serum alanine aminotransferase (ALT) level is a critical parameter for evaluating liver injury in non-alcoholic fatty liver disease (NAFLD). However, the currently accepted upper limits of normal (ULN) for serum ALT (ULN-ALT) are debated, as they may be excessively high. METHODS: A total of 1638 children aged 6-16 years, comprising 507 children with normal BMI (500 healthy children and 7 children with NAFLD), 199 overweight children, and 932 obese children, were included in the analysis. We re-evaluated the ULN-ALT in 500 healthy Chinese children using the 95th percentiles of serum ALT levels as revised ULN-ALT. Fatty liver was identified by ultrasound examination. RESULTS: Significant positive correlations between serum ALT levels and body mass index (BMI) were detected in overweight boys (r = .399, P < .001), obese boys (r = .398, P < .001), and obese girls (r = .392, P < .001). The prevalence percentages of NAFLD were 93.6%, 75.8%, and 37.9% in obese boys with serum ALT levels of >50, 25-50, and ≤25 U/L and were 81.6%, 67.9%, and 20.6% in obese girls with serum ALT levels of >40, 20-40, and ≤20 U/L, respectively. CONCLUSION: Serum ALT levels significantly correlated with abnormal BMI values in children, suggesting a rigorous BMI threshold is needed to establish the cutoffs for serum ULN-ALT in children. Besides, the revised serum ULN-ALT can uncover mild liver injury in obese children with NAFLD.