The underlying mechanisms for the "isolated positivity for the hepatitis B surface antigen (HBsAg)" serological profile.

During HBV infection, four structural antigen/antibody systems are observed: hepatitis B surface antigen (HBsAg) and its antibody (anti-HBs); the pre-S antigens associated with HBsAg particles and their antibodies; the particulate nucleocapsid antigen (HBcAg) and anti-HBc; and an antigen structurally related to HBcAg, namely HBeAg and its antibody (anti-HBe). Through the examination of this antigen-antibodies system, hepatitis B infection is diagnosed and the course of the disorder may be observed. Isolated HBsAg seropositivity is a peculiar serological pattern in HBV infection observed some times in routine laboratory. In most cases is not clear how this profile should be interpreted neither its significance. This pattern, however, may be associated with some clinical and laboratorial situations of great relevance, some of which will be addressed in this article.