HCV Ag highly correlated with HCV RNA in HCV/HBV co-infection (log HCV RNA = 2.44 + 1.08 [log HCV Ag], R2 = 0.968, p = 0.002), while correlation of these two markers between mono-infection and co-infection was not significantly different (p = 0.119). This evidence concerns the gene RENBP and coinfection.