What does a positive HBsAg indicate?

A positive HBsAg (Hepatitis B surface Antigen) indicates the presence of the Hepatitis B virus in the bloodstream and signifies an active infection. This antigen is a protein on the surface of the virus and is produced when the virus is replicating within the body. Therefore, its presence typically suggests either an acute or chronic Hepatitis B infection.

In the context of the options provided, a positive HBsAg is directly linked to chronic infection, indicating that the virus is ongoing in the body. This is important for clinical decision-making, as individuals with chronic infection may require long-term monitoring and management to prevent complications related to liver disease.

Other options, such as vaccination immunity or resolved infection, would be indicated by the presence of antibodies rather than the antigen itself, and natural immunity describes a previous infection that has resolved, which would not show a positive HBsAg. Thus, the correct understanding of HBsAg is crucial for diagnosing and managing Hepatitis B infections effectively.