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Hepatitis Serology Testing

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Overview

Serological tests involving the measurement of antigens and antibodies can help with identifying infection with hepatitis along with whether it is acute or chronic, as well as if the patient is immune or not.

Antigens

An antigen is a protein found on the virus which can stimulate an immune response. Key antigens found are:

  • Surface antigens (sAg):
    • Indicates the presence of the virus
    • Acute if present for 1-10 weeks following exposure
    • Chronic if present for >6 months
  • Core antigens (cAg):
    • Indicates the body is producing antibodies against the virus
    • Modified core antigens (eAg):
    • Indicates the virus is actively replicating

For example, in hepatitis B, the following antigens may be present:

  • HBsAg – hepatitis B surface antigen:
    • Suggests present infection
  • HBcAg – hepatitis core antigen:
    • Suggests the body is producing antibodies against hepatitis B
  • HBeAg:
    • Suggests that hepatitis B is actively replicating

Antibodies

Antibodies are produced in response to the antigen. Two key types are:

  • IgM:
    • This is produced as the body’s first response to non-self-antigens and decreases as IgG production begins.
    • This is the immediate response
  • IgG:
    • Specific IgG antibodies are released a few weeks after the initial infection and some remain after infection, giving immunity.
    • This is the chronic response

For example, in hepatitis B, the following antibodies may be present:

  • Anti-HBs antibody: antibodies against the surface antigen
    • This can suggest that the person has an acute infection, has had a previous infection, or has been immunised (as surface antigens are used in vaccination) as it can persist for life.
  • Anti-HBc antibody: antibodies against the core antigen
    • This is only present in acute infection or a previous infection. It is never seen post-vaccination as core antigens are not used in vaccines.
  • Anti-HBe antibody: these antibodies reduce infectibility

Example Interpretation

Using these principles, we can determine the nature of a patient’s infection. The following table summarises typical findings for hepatitis B serology:

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