In hepatitis B infection, which serologic marker indicates acute infection?

• A. HBsAg
• B. Anti-HBs
• C. Anti-HBc IgM
• D. HBeAg

Answer: (C)

Anti-HBc IgM signals acute hepatitis B infection because IgM antibodies to the core antigen appear early during the initial infection and indicate a recent exposure. They rise in the acute phase and typically wane as the infection resolves, whereas anti-HBc IgG persists long-term in past or chronic infection. Other markers tell different things: HBsAg shows ongoing infection (acute or chronic) but doesn’t specify the timing; anti-HBs indicates immunity from vaccination or recovery; and HBeAg reflects active viral replication and high infectivity, not necessarily whether the infection is acute.