## Most Common Initial Marker in Acute HBV Infection **Key Point:** HBsAg is the first detectable marker in acute hepatitis B infection and remains the most reliable screening test for HBV exposure. ### Timeline of Serological Markers | Marker | Appears | Peak | Disappears | Significance | |--------|---------|------|------------|-------------| | **HBsAg** | 1–10 weeks (earliest) | Week 4–6 | 4–6 months (acute) | First marker; indicates active infection | | **Anti-HBc IgM** | Week 1–2 | Week 3–4 | 6 months | Confirms acute infection; diagnostic | | **HBeAg** | Shortly after HBsAg | Week 2–3 | 1–2 weeks | High viral replication; infectivity | | **Anti-HBs** | After HBsAg clearance | Months | Persists | Recovery; immunity | **High-Yield:** HBsAg is present in: - Acute HBV infection (transient) - Chronic HBV infection (persistent >6 months) - Resolved infection with anti-HBc (rare; occult HBV) **Clinical Pearl:** In a patient with acute jaundice and suspected HBV, HBsAg positivity + anti-HBc IgM positivity = acute HBV infection (diagnostic). HBsAg alone (without IgM) = either acute late-phase or chronic infection. ### Why HBsAg is the Most Common Initial Marker 1. **Earliest detection:** Appears within 1–10 weeks of exposure, before symptoms 2. **Highest sensitivity in screening:** Present in >95% of HBV-infected individuals 3. **Persists longest:** Detectable throughout acute phase and into chronic phase 4. **Practical:** Routine screening test in all blood banks, prenatal programs, and occupational health [cite:Harrison 21e Ch 304]
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