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- Hepatitis testing is usually an antibody test (for example, anti-HAV, anti-HCV, etc.)
- Hepatitis B testing is more complex as there are tests for antigens and antibodies to three different viral proteins
- HBsAg or hepatitis B surface antigen (not antibody) indicates hepatitis B infection. This is the most sensitive test for ongoing hepatitis B infection; even better than PCR
- Anti-HBs or hepatitis B surface antibody indicates immunity to hepatitis B either through resolved infection or successful vaccination
- Anti-HBc or hepatitis B core antibody indicates infection (current or resolved)
- For every complete hepatitis B viral particle, there are many more incomplete viral particles (spheres and filaments) that do not contain viral DNA
- HBsAg (surface antigen) is on the surface or envelope of the complete virus and also on the incomplete viral particles
- HBsAg is more sensitive than PCR (HBV DNA) testing. If HBsAg is positive but HBV DNA is negative, hepatitis B infection is still present
- Anti-HBs (surface antibody) is only detectable when hepatitis B infection has resolved. It is also positive after successful vaccination of an individual that was never infected
- Core, part of the nucleocapsid, is found in the complete viral particle, not the vaccine. Core protein is not secreted into serum but anti-HBc (core antibody) can be detected in serum and is a very good test for hepatitis B infection, either ongoing or resolved
- Exception: hepatitis B infection can rarely persist even when HBsAg is negative. This is called "occult hepatitis B" infection.
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