Validation study of age-independent fibrosis score (Fibrosis-3 index) in patients with metabolic dysfunction-associated steatotic liver disease

Background and Aims: Because the accuracy of the Fibrosis-4 (FIB-4) index for predicting liver fibrosis changes with age, the need for different cut-offs in various age groups has frequently been discussed. We developed the age-independent score, the Fibrosis-3 (FIB-3) index, and have shown its usefulness in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). This study aimed to validate the diagnostic ability of the FIB-3 index to predict fibrosis progression using a large new patient cohort. Methods: The ability of the FIB-3 index to predict liver fibrosis was analyzed by comparing it with that of the FIB-4 index using data from 1398 patients with MASLD enrolled in the Asia-based clinical outcome NAFLD study. Results: The areas under the receiver operating characteristic curves for predicting fibrosis stage F3 or higher were not different between the FIB-3 and FIB-4 indices in the entire cohort. Using the single ideal cut-offs of the indices (3.41 for FIB-3 index and 2.01 for FIB-4 index), the predictive accuracy of the FIB-3 index was not significantly different from that of the FIB-4 index among patients aged <60 years; however, the accuracy of the FIB-3 index was significantly higher than that of the FIB-4 index in those aged >= 60 years (0.645 and 0.529, respectively; p < 0.0001). Conclusion: The high ability of the FIB-3 index with a single cut-off to predict liver fibrosis in patients with MASLD was confirmed. The FIB-3 index could serve as a useful tool for assessing liver fibrosis regardless of age.