C4A and primary biliary cholangitis: The strong correlation between circulating FGF19 and C4, liver fibrosis stage, and the degree of cholestasis (as reflected by TBA and bilirubin) (Figures 2(b)–2(d)) in PBC-AIH OS patients indicates the regulation of BA synthesis (mediated via CYP7A1) is still controlled by circulating FGF19.