## Serological Pattern in Chronic Hepatitis B **Key Point:** Chronic HBV infection is defined by persistence of HBsAg for >6 months. The most common serological pattern is HBsAg+, anti-HBc+, anti-HBc IgM–. ### Serological Patterns and Their Interpretation | Pattern | HBsAg | Anti-HBc | Anti-HBc IgM | Anti-HBs | Interpretation | |---------|-------|----------|--------------|----------|----------------| | **Acute HBV (early)** | + | ± | + | − | Acute infection, early phase | | **Acute HBV (late)** | + | + | + | − | Acute infection, late phase | | **Chronic HBV** | + | + | − | − | **Chronic infection (most common)** | | **Resolved HBV** | − | + | − | + | Past infection, immune | | **Vaccinated/Immune** | − | − | − | + | Immunity from vaccine | | **Occult HBV** | − | + | − | − | Latent infection (rare) | **High-Yield:** The presence of **anti-HBc IgM is the key differentiator**: - **Positive anti-HBc IgM** = Acute infection (regardless of HBsAg status) - **Negative anti-HBc IgM + HBsAg+** = Chronic infection ### Why This Pattern is Most Common in Chronic HBV 1. **HBsAg persistence:** Remains positive >6 months (definition of chronicity) 2. **Anti-HBc positivity:** Indicates past or ongoing exposure; develops early and persists lifelong 3. **Anti-HBc IgM negativity:** IgM wanes after 6 months; its absence confirms chronic (not acute) phase 4. **Anti-HBs absence:** Does not develop while HBsAg is present (mutually exclusive in most cases) **Clinical Pearl:** In blood bank screening, a donor with HBsAg+ should be tested for anti-HBc IgM to exclude acute infection. If IgM is negative, the donor is a chronic carrier and is permanently deferred from donation. **Mnemonic:** **"CAB" for Chronic HBV** - **C**hronic: HBsAg persists >6 months - **A**nti-HBc: Always positive (lifelong marker of exposure) - **B**ut no IgM: IgM is absent (distinguishes from acute) [cite:Harrison 21e Ch 304]
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