Validation of a cholangiographic prognostic model in primary sclerosing cholangitis

Background and study aims: We previously developed a prognostic model for primary sclerosing cholangitis (PSC), which was primarily based on a cholangiographic classification of the intra- and extrahepatic biliary tree lesions. The aim of the present study was to validate the performance of this model in an external cohort. Patients and methods: The validation dataset consisted of patients with PSC from a single referral center in Oslo, Norway. The patients' cholangiograms were scored according to the Amsterdam classification. We then examined whether adjusting the value of the original coefficients of the predictors or adding new predictors would improve the fit of the original model in the validation cohort. In addition, we evaluated calibration (closeness between observed and expected survival) and discrimination using the concordance index. Results: A total of 111 patients (mean age 35 +/- 13 years; 76% male) were included in the validation study. Baseline clinical characteristics were comparable between the two cohorts. None of the coefficients that were re-estimated in the validation cohort differed significantly from the values of the original model. Observed and expected survival curves were in close agreement across different risk groups. Discrimination of the original model was preserved in the validation cohort: the concordance index was the same in both cohorts. Conclusions: The prognostic model showed adequate performance in an independent series of patients. Therefore, we updated the model using the data from both cohorts to provide more robust estimates of transplant-free survival for individual patients. A nomogram was constructed, which can be used to predict medium-and long-term prognosis in individual patients with PSC.