Which serologic marker indicates active hepatitis B infection?

Which serologic marker indicates active hepatitis B infection?

• A. HBsAg negative
• B. HBsAg positive
• C. IgG anti-HBc positive
• D. IgM anti-HBc positive

Answer: (B)

In hepatitis B serology, the presence of the hepatitis B surface antigen (HBsAg) in the blood indicates an active infection because the virus is circulating and replicating. This marker shows that the person is currently infected and potentially infectious. If HBsAg is not detected, it could mean there’s no active infection, or the person could be in a window period where HBsAg has disappeared but other markers (like IgM anti-HBc) may still be present. IgM anti-HBc points to a recent or acute infection, but the direct sign of ongoing viral replication and infectivity is HBsAg. IgG anti-HBc reflects prior exposure and may persist in chronic infection, but by itself does not prove active replication. Anti-HBs indicates immunity from recovery or vaccination and does not signify current infection.

In hepatitis B serology, the presence of the hepatitis B surface antigen (HBsAg) in the blood indicates an active infection because the virus is circulating and replicating. This marker shows that the person is currently infected and potentially infectious. If HBsAg is not detected, it could mean there’s no active infection, or the person could be in a window period where HBsAg has disappeared but other markers (like IgM anti-HBc) may still be present.

IgM anti-HBc points to a recent or acute infection, but the direct sign of ongoing viral replication and infectivity is HBsAg. IgG anti-HBc reflects prior exposure and may persist in chronic infection, but by itself does not prove active replication. Anti-HBs indicates immunity from recovery or vaccination and does not signify current infection.