Assays for Hepatitis B Virus

Abstract

Along the course of a typical hepatitis B virus (HBV) infection, three viral antigens appear in patients’ serum: surface antigen (HBsAg), core antigen (HBcAg) and e antigen (HBeAg) (Figure 1). The host, in response to the infection, sooner or later produces corresponding antibodies, anti-HBs, anti-HBc and anti-HBe. All these antigens and antibodies have been used as diagnostic markers to determine the status of HBV infection: thus, HBsAg indicates current infection (2,17) while anti-HBs signifies immunity of the patient to HBV (5). The presence of detectable amounts of HBcAg (as Dane particles) (1,4) or HBeAg (12,13,14) reflects high concentrations of HBV and high infectivity; and anti-HBe, on the other hand, often coincides with lower levels of HBV and infectivity (Table 1). Anti-HBc (6,15) generally coexists with HBsAg or anti-HBs and therefore is a marker for current or past infection. When anti-HBc is the only HBV marker, it indicates one of two possibilities: 1) Current infection with HBV with HBsAg at a level too low to be detected; 2) Very early or very late convalescence with anti-HBs at a level too low for detection. A test for IgM class anti-HBc should be helpful to distinguish between early or late stage of convalescence (16). In HBsAg positives, the levels of the IgM antibody also distinguish recent infection or long-term chronic infection (Figure 2). Commercial diagnostic kits are available for all the above serological markers of HBV except for HBcAg.