In patients with nonalcoholic fatty liver disease (NAFLD), liver fibrosis is the predictive factor for liver-related events and prognosis. This retrospective study aimed to evaluate longitudinal changes in the FIB-4 index and to determine a strategy for diagnosing and following patients with NAFLD using this index. We analyzed the FIB-4 index at baseline and after 1 and 5 years in 272 consecutive patients with biopsy-proven NAFLD. Of these, 52 patients underwent serial biopsies. The change in the FIB-4 index was correlated with changes in the fibrosis stage among these patients (p = 0.048). The median FIB-4 index was 1.64 at baseline, 1.45 at 1 year, and 1.74 at 5 years. The negative predictive value for advanced fibrosis at a low cutoff point was 90.4/90.1 at baseline/1 year. Its specificity at a high cutoff point increased from 65.0% at baseline to 82.3% at 1 year. Multivariate analysis identified the FIB-4 index at 1 year as a predictive factor for a FIB-4 index > 2.67 at 5 years. A FIB-4 index < 1.30 was acceptable for excluding advanced fibrosis at baseline. In contrast, to evaluate and predict advanced liver fibrosis with the FIB-4 index at a high cutoff point, we should use the index at 1 year after appropriate therapy.
