Hepatitis B surface antigen (HBsAg)

This is a protein antigen produced by Hepatitis B Virus (HBV). This antigen is the earliest indicator of acute hepatitis B infection and frequently identifies infected people before symptoms appear. HBsAg disappears from the blood during the recovery period. In some people (particularly those infected as children or those with a weakened immune system, such as those with AIDS), chronic infection with HBV may occur and HBsAg then remains positive. HBsAg is also positive in people who are said to be carriers (ie they have low levels of virus present but are not infectious to others).

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