What is Anti-HBc (Hepatitis B Core Antibody)?
Anti-HBc is an antibody directed against the hepatitis B core antigen (HBcAg) that appears 1-2 weeks after HBsAg during acute HBV infection and typically persists for life, serving as a marker of past or current HBV infection. 1
Key Characteristics
Anti-HBc has two forms with distinct clinical meanings:
IgM anti-HBc: Appears at the onset of acute hepatitis B symptoms and persists for up to 6 months if the infection resolves. This form indicates acute or recent HBV infection 1, 2
IgG anti-HBc: Predominates after the IgM phase and remains detectable for lengthy periods, often lifelong. This form indicates past infection 1
Clinical Interpretation
The presence of anti-HBc must be interpreted alongside other HBV markers:
When combined with HBsAg positive:
When HBsAg is negative:
- Anti-HBc positive + anti-HBs positive = recovered from past infection and immune 1, 2
- Anti-HBc positive alone (isolated anti-HBc) = may indicate past infection with waned anti-HBs, false-positive result, low-level chronic infection, or passive transfer to infant from HBsAg-positive mother 1, 2
Important Clinical Pitfalls
The "window period": Anti-HBc IgM may be the only detectable marker during the interval between HBsAg disappearance and anti-HBs appearance in resolving acute infection 3
Isolated anti-HBc interpretation varies by population prevalence:
- In high HBV prevalence populations: likely indicates previous infection with loss of anti-HBs 1, 4
- In low HBV prevalence populations: often represents a false-positive result (found in 10-20% of persons with HBV serologic markers) 4
Chronic infection nuance: In chronic HBV infection, IgM anti-HBc can persist at low levels during viral replication, though typically not detectable by U.S. assays. However, exacerbations of chronic infection can cause positive IgM anti-HBc tests 4
Distinction from Vaccination
Persons who recover from natural HBV infection are positive for both anti-HBs and anti-HBc, whereas persons who respond to hepatitis B vaccine are positive only for anti-HBs (no anti-HBc) 1, 4. This distinction is critical for differentiating natural immunity from vaccine-induced immunity.
Infectivity Considerations
Persons with isolated anti-HBc have HBV DNA detected in <10% of cases and are unlikely to transmit infection except under circumstances involving direct percutaneous exposure to large quantities of blood (e.g., blood transfusion or organ transplantation) 1, 4. These individuals can experience HBV reactivation during chemotherapy or immunosuppressive therapy, with reappearance of HBsAg 1.