Background & AimsFontan-type surgery is used as a palliation for congenital heart disease with univentricular physiology but may, in the long term, lead to advanced chronic liver disease. This study assessed the accuracy of conventional non-invasive models in assessing liver fibrosis and introduces a new risk score employing non-invasive tools. MethodsA prospective, cross-sectional, observational study was conducted across five European centers and encompassing all consecutive adult patients with Fontan circulation, liver biopsy and non-invasive tests (elastography, APRI, FIB-4, Fibrosis score, Doha, GUCI, and AAR). The primary outcome was the identification of severe liver fibrosis on biopsy. Multivariable logistic regression identified non-invasive predictors of severe fibrosis, leading to the development and internal validation of a new scoring model named the FonLiver risk score. ResultsIn total, 217 patients (mean [standard deviation] age, 27.9 [8.9] years; 50.7% males) were included. Severe liver fibrosis was present in 47.9% (95% CI 41.2%–54.5%) and correlated with a lower functional class, protein-losing enteropathy, and compromised cardiopulmonary and systemic hemodynamics. The final FonLiver risk score incorporated liver stiffness measurement using transient elastography and platelet count and demonstrated strong discrimination and calibration (area under the receiver operating curve [AUROC] of 0.81). The FonLiver risk score outperformed conventional prediction models (APRI, FIB-4, Fibrosis score, Doha, GUCI, and AAR), which all exhibited worse performance in our cohort (AUROC < 0.70 for all). ConclusionSevere liver fibrosis is prevalent in adults following Fontan-type palliation and can be effectively estimated using with the novel FonLiver risk score. This scoring system can be easily incorporated into the routine assessment of patients with Fontan circulation.