Which serological marker indicates CHRONIC hepatitis B infection?

Correct answer: C. HBsAg persisting for more than six months

• A. Anti-HBc IgM indicates RECENT ACUTE infection. It is also the sole marker present during the 'window period', when HBsAg has cleared but anti-HBs has not yet appeared.
• B. Anti-HBe indicates reduced viral replication and lower infectivity. It reflects a phase of infection rather than defining chronicity.
• C. CORRECT. HEPATITIS B SURFACE ANTIGEN (HBsAg) is the marker of ACTIVE infection, and its persistence BEYOND SIX MONTHS is the definition of chronic hepatitis B. A patient who remains HBsAg-positive at six months is a chronic carrier, is infectious, and requires standard precautions plus medical follow-up for the risks of cirrhosis and hepatocellular carcinoma.
• D. Anti-HBs indicates IMMUNITY — from resolved infection or from vaccination. Its presence is essentially incompatible with chronic infection.

Note: Read hepatitis B panels by asking three questions in order. Is HBsAg present? (active infection). Is anti-HBs present? (immunity). Is anti-HBc present, and is it IgM or IgG? (past or present natural exposure — anti-HBc is ABSENT after vaccination, which is what distinguishes the vaccinated patient from the recovered one.)