RBP4 and chronic hepatitis C virus infection: Serum RBP4 could be linked to HSC by transporting vitamin A. There is a negative correlation between the level of plasma RBP4 and the order of severity of histological fibrosis, activity, and steatosis, which may be related to vitamin A. RBP4 can diagnose advanced fibrosis grades in patients with underlying chronic hepatitis C (73).