The first serologic marker to appear in acute hepatitis B virus infection is which of the following?

• A. Anti-HB
• B. Anti-HBc
• C. Anti-HBe
• D. HBsAg

Answer: (D)

The first serologic signal in acute hepatitis B is the viral surface antigen appearing in the blood. This antigen is produced by the virus and shows up early during replication, before the immune system has made antibodies. Its presence confirms active infection and indicates that the person is infectious. As the immune response progresses, antibodies develop—anti-HBc IgM around symptom onset, followed by others like anti-HBe and eventually anti-HBs after recovery or vaccination. In the brief window period when HBsAg has disappeared but anti-HBs is not yet present, anti-HBc IgM can be the marker observed. But overall, the initial marker you see in acute HBV infection is the surface antigen.