The serum alanine aminotransferase (ALT) level is considered an important parameter for determining liver injury in patients with non-alcoholic fatty liver disease (NAFLD). Nevertheless, owing to the fact that currently upper limits of normal (ULN) for serum ALT (ULN-ALT) are excessively high, their acceptance is questionable. 

A total of 1638 children, aged 6-16 years participated in the trial, among which 507 children had normal body mass index (BMI) with 500 as healthy children and 7 children suffering with NAFLD, 199 overweight children, and 932 obese children. The ULN-ALT was re-investigated in 500 healthy children using the 95th percentiles of serum ALT levels as revised ULN-ALT. The diagnosis of fatty liver was performed by ultrasound examination.

The outcome of the trial showed a strong positive correlation between serum ALT levels and BMI in overweight boys, obese boys, and obese girls. The prevalence of NAFLD was found to be 93.6%, 75.8%, and 37.9% in obese boys with serum ALT levels of >50, 25-50, and ≤25 U/L. Moreover, in obese girls, it was 81.6%, 67.9%, and 20.6% with serum ALT levels of >40, 20-40, and ≤20 U/L, respectively.

Hence, evidence supports a strong association of serum ALT levels with abnormal BMI values in children. This, in turn, indicates that a stringent BMI threshold is required to establish the upper limit for serum ULN-ALT in children. In addition, the revised serum ULN-ALT can facilitate even identification of mild liver injury in obese children with NAFLD.

Source: Lu Y, Wang Q, Yu L, et al. Revision of serum ALT upper limits of normal facilitates assessment of mild liver injury in obese children with non-alcoholic fatty liver disease [published online ahead of print, 2020 Apr 8]. J Clin Lab Anal. 2020;34(7):e23285.