Chronic delta hepatitis: detection of hepatitis delta virus antigen in serum by immunoblot and correlation with other markers of delta viral replication.

To investigate the presence of serum hepatitis delta virus antigen by immunoblot and its correlation with other markers of active viral replication (intrahepatic hepatitis D antigen, IgM antibody to hepatitis D and serum hepatitis D virus RNA), we studied serum samples from 50 patients with chronic hepatitis D virus infection (38 with and 12 without intrahepatic hepatitis D antigen). Of the 38 patients with intrahepatic hepatitis D antigen, 27 (71%) had antigen detectable in serum by immunoblot, whereas only two were reactive by conventional enzyme-linked immunosorbent assay. Thirty-one (82%) patients were also positive for serum hepatitis D virus RNA by spot hybridization and 33 (87%) were positive for IgM anti-hepatitis D virus. All markers were simultaneously present in 24 patients. Circulating hepatitis D antigen was detected in one (8%), IgM anti-hepatitis D in seven (58%) and hepatitis D virus RNA in two (17%) of the 12 patients who had anti-hepatitis D in serum but not detectable hepatitis D antigen in liver. Hepatitis D antigen was not detected in serum of any of the 15 control patients. The results suggest that serum hepatitis D antigen as detected by immunoblot and serum hepatitis D virus RNA are similar in sensitivity for detection of active hepatitis D virus replication during chronic infection and constitute useful, sensitive and noninvasive tests for the diagnosis and monitoring of chronic hepatitis D virus infection.