Question
Laboratory diagnosis of acute hepatitis B infection
Answer
Laboratory diagnosis of acute Hepatitis B infection:
- HBsAg — the first marker to appear, indicating current infection.
- IgM anti-HBc — indicates recent/acute infection; a key marker, since it is the only detectable marker during the “window period” (when HBsAg has already cleared but anti-HBs has not yet risen) — its presence is the most reliable indicator of a genuinely acute (rather than chronic) infection, since IgG anti-HBc (which persists in chronic infection too) cannot distinguish acute from chronic disease on its own.
- HBeAg — indicates active viral replication and high infectivity, typically present in acute infection.
- HBV DNA (quantitative PCR) — the most direct marker of active viral replication.
- Liver function tests — raised ALT/AST reflecting acute hepatocellular injury; raised bilirubin.
Typical acute infection pattern: HBsAg positive, IgM anti-HBc positive, HBeAg positive (usually), HBV DNA detectable, with anti-HBs still negative (anti-HBs appears later, on recovery). Resolution of acute infection is marked by clearance of HBsAg and HBeAg, seroconversion to anti-HBs and anti-HBe, and persistence of IgG anti-HBc (replacing IgM) as a lifelong marker of past infection.
Distinguishing acute from chronic infection: IgM anti-HBc is the key discriminator — positive in acute infection (and in acute flares of chronic infection), but typically negative or low-titre in established chronic infection, where IgG anti-HBc dominates instead; persistence of HBsAg beyond 6 months defines progression to chronic infection.