FGF21 and fatty liver disease: Although the aforementioned studies suggest that FGF21 could be a potential biomarker to screen or monitor NAFLD patients [23], the methods utilized to assess the severity of hepatic steatosis, such as B-mode ultrasound or pathological score system, were qualitative or semi-quantitative and did not reflect the quantitative association between serum FGF21 and hepatic fat content accurately.