A laboratory report shows HBsAg negative, anti-HBs negative, and anti-HBc IgM strongly positive in a jaundiced adult. During this 'window period' of hepatitis B infection, why does anti-HBc IgM serve as the diagnostic marker?
- A It persists after HBsAg disappears but before anti-HBs becomes detectable, marking ongoing recent infection ✓
- B It appears earliest of all serological markers and remains detectable throughout life
- C It indicates immunity from past vaccination combined with occult infection
- D It signals chronic carrier state because core antibody never clears from serum
Correct answer: A. It persists after HBsAg disappears but before anti-HBs becomes detectable, marking ongoing recent infection
Explanation
The window period spans the interval when HBsAg has been cleared from blood but protective anti-HBs has not yet appeared. Anti-HBc IgM rises early in acute infection and persists for several months, making it the only routinely detectable marker during this gap and the key evidence of recent infection. Anti-HBc IgG, not IgM, persists lifelong, and vaccination alone produces anti-HBs without any anti-HBc response.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.