Fibrotic NASH in Individuals with Obesity: a Cross-sectional Analysis of the Prevalence of this Significant Milestone of Disease Progression and Accuracy of a Non-invasive Marker for its Screening

Background Fibrotic non-alcoholic steatohepatitis (NASH), i.e., the concomitant presence of active inflammation and fibrosis, represents a milestone in the natural history of NAFLD and a critical time point in its progression. The purpose of this study was to analyze the diagnostic accuracy of the non-invasive Fibrotic NASH Index (FNI) in individuals with obesity undergoing bariatric surgery. Methods This is a cross-sectional study, enrolling individuals who underwent bariatric surgery with liver biopsy at a tertiary university hospital. FNI was calculated, and a cutoff value was determined. Its diagnostic accuracy was then calculated through comparison with the gold standard test for this analysis (histopathological examination). Results Of 128 participants, 83.6% were female, and the average age was 39.8 ± 8.7 years. The mean BMI was 38.7 ± 5.7 kg/m 2 . NAFLD was histologically confirmed in 76.6%, of which 81.6% had NASH. Histologically confirmed fibrotic NASH was observed in 22.7% of the general study population, 29.6% of individuals with NAFLD, and 36.3% of those with NASH. The mean FNI was 0.18 ± 0.19. An optimal cutoff point of 0.21 was determined, with an overall accuracy of 90.1%, an 82.8% sensitivity, a 90.8% specificity, a 72.6% positive predictive value, and a 94.7% negative predictive value. Conclusions FNI provided adequate accuracy in detecting and ruling out fibrotic NASH. Considering the importance of fibrotic NASH within the natural history of NAFLD progression and the fact that this marker uses simple variables, it may be of great importance in high-risk populations, and its external validation and use should be encouraged. Graphical Abstract