MicrobiologyVirologyhigh-yield
Reading hepatitis B serology like a table
Interpret HBsAg, anti-HBs and anti-HBc across acute, chronic, resolved, immunised and window states, plus a line each on hepatitis C, A and E.
6 min read · updated 2026-08-24
What each marker actually means
Do not memorise the states — build them from what each marker is, and the table falls out.
- HBsAg (surface antigen) — the virus is present. Positive = current infection (acute or chronic). It is the first marker to appear.
- Anti-HBs (antibody to surface) — immunity, from either recovery or vaccination. It is the last marker to appear in natural infection.
- Anti-HBc (antibody to core) — exposure has occurred. The core antigen is never in the vaccine, so anti-HBc is the single marker that separates natural infection from vaccination.
- IgM anti-HBc = recent/acute (and the only positive in the window period).
- IgG anti-HBc = past or chronic exposure.
- HBeAg — secreted during active viral replication; marks high infectivity. Anti-HBe = falling replication (or a precore mutant — worth remembering).
The states as one table
| State | HBsAg | Anti-HBs | Anti-HBc (IgM / IgG) | HBeAg |
|---|---|---|---|---|
| Acute infection | + | − | IgM + | + |
| Window period | − | − | IgM + (sole marker) | − |
| Chronic infection | + (>6 months) | − | IgG + | + or − |
| Resolved / past infection | − | + | IgG + | − |
| Immunised (vaccine) | − | + | − (never) | − |
The two traps examiners love
- Window period — HBsAg has cleared but anti-HBs has not yet risen. Everything reads negative except IgM anti-HBc, which is why anti-HBc is included in blood-donor screening. A "recent needle-stick, all negative but IgM anti-HBc positive" stem is this.
- Vaccinated vs recovered — both have anti-HBs. Only the recovered patient also has anti-HBc (natural core exposure). Isolated anti-HBs = vaccine.
HBsAg persisting beyond 6 months = chronic, by definition. HBeAg tells you infectivity/replication, not chronicity.
The other hepatitides in one line each
| Virus | High-yield point |
|---|---|
| Hepatitis C | Anti-HCV = exposure, not clearance; confirm active infection with HCV RNA (PCR). Most likely to chronify. |
| Hepatitis A | Faeco-oral, self-limiting; IgM anti-HAV = acute, IgG = past/immune. No chronic state. |
| Hepatitis E | Faeco-oral; fulminant in pregnancy (high mortality, esp. 3rd trimester); IgM anti-HEV = acute. |
Pearl: anti-HBc is the honest witness — it is the only marker that knows whether the immune system met the real virus or just the vaccine.
Sources
- Ananthanarayan and Paniker's Textbook of Microbiology, 11e
- Harrison's Principles of Internal Medicine, 21e