Hepatitis B

Hep B is important in rheumatology. It has to be screened for before biologic drugs are used for rheumatoid arthritis or PsA. 3 tests are done:

• Hep B surface antigen
• Hep B surface ab
• Hep B core ab IgM and IgG abs

Core ab pos

Hepatitis B core antigen (HBcAg) is an intracellular antigen that is expressed in infected hepatocytes. It is not detectable in serum with available commercial assays. Anti-HBc can be detected throughout the course of HBV infection. During acute infection, anti-HBc is predominantly of IgM class. IgM anti-HBc is the sole marker of HBV infection during the window period between the disappearance of HBsAg and the appearance of anti-HBs. The detection of IgM anti-HBc is usually regarded as an indication of acute HBV infection. However, IgM anti-HBc may remain detectable up to two years after the acute infection. Furthermore, the titer of IgM anti-HBc may increase to detectable levels during exacerbations of chronic hepatitis B. This can present a diagnostic problem: incorrectly suggesting acute hepatitis B, particularly in endemic areas in which many HBsAg-positive patients presenting with acute hepatitis actually have exacerbations of chronic hepatitis B. Other common causes of acute exacerbation of chronic hepatitis B are superinfection with hepatitis D virus (delta virus) or hepatitis C virus. IgG anti-HBc persists along with anti-HBs in patients who recover from acute hepatitis B. It also persists in association with HBsAg in those who progress to chronic HBV infection. Tests for IgG anti-HBc are not commercially available, so total anti-HBc is measured when screening or testing for chronic HBV. Some investigators have noted a correlation between the titer of IgM anti-HBc and serum alanine aminotransferase, serum HBV DNA levels and histologic inflammation in patients with chronic hepatitis B. However, the studies correlating IgM anti-HBc titer with HBV replication or activity of liver disease were performed using quantitative IgM anti-HBc assays that have lower cutoffs than the qualitative assays available in the United States. The latter assays were designed for diagnosis of acute HBV infection and have higher cutoffs. [1]