What does a positive Hepatitis B (HBV) core antibody test result indicate?

Understanding a Positive Hepatitis B Core Antibody (Anti-HBc) Test Result

A positive hepatitis B core antibody (anti-HBc) test indicates previous exposure to the hepatitis B virus (HBV), which could represent either a past infection that has resolved, an ongoing chronic infection, or rarely, an acute infection in the "window period." 1 The interpretation depends on the results of other HBV serologic markers.

Interpretation of Positive Anti-HBc Based on Other Serologic Markers

Scenario 1: Anti-HBc Positive + HBsAg Negative + Anti-HBs Positive

• Interpretation: Resolved past HBV infection with immunity 1
• This is the most common scenario for a positive anti-HBc result
• The person has recovered from a previous HBV infection and developed natural immunity
• No further testing is required 1

Scenario 2: Anti-HBc Positive + HBsAg Positive + IgM Anti-HBc Positive

• Interpretation: Acute HBV infection 1
• High infectivity and risk of transmission
• Requires medical monitoring and possibly treatment

Scenario 3: Anti-HBc Positive + HBsAg Positive + IgM Anti-HBc Negative

• Interpretation: Chronic HBV infection 1
• Person is infectious and at risk for long-term complications
• Requires medical evaluation and possible treatment

Scenario 4: Anti-HBc Positive + HBsAg Negative + Anti-HBs Negative

• Interpretation: Four possibilities 1:
  1. Resolved infection with waning anti-HBs levels (most common)
  2. False-positive anti-HBc test result
  3. "Low-level" chronic HBV infection (occult HBV)
  4. Window period of acute infection (between disappearance of HBsAg and appearance of anti-HBs)

Clinical Significance and Management

For Isolated Anti-HBc (Scenario 4)

• HBV DNA testing may help determine if occult infection is present 1
• Hepatitis B vaccination can help distinguish between possibilities:
  • Anamnestic response (rapid anti-HBs development within 2 weeks) suggests previous infection with immunity 2
  • Normal vaccine response suggests false-positive anti-HBc 2
  • Failure to respond may indicate occult chronic infection

For Healthcare Settings

• Patients with positive anti-HBc who are also anti-HBs positive (>10 IU/mL) are considered immune from prior infection 1
• In dialysis settings, these patients require no further testing 1
• For transplantation, positive anti-HBc donors require special consideration due to risk of viral reactivation in immunosuppressed recipients 1

For Cancer Patients

• Patients who are HBcAb positive are at risk for HBV reactivation during immunosuppressive therapy, particularly with anti-CD20/CD52 monoclonal antibodies 1
• Prophylactic antiviral therapy may be indicated before starting immunosuppressive treatment

Common Pitfalls to Avoid

1. Misinterpreting isolated anti-HBc: Don't assume chronic infection without additional testing
2. Missing the window period: During acute infection resolution, HBsAg may disappear before anti-HBs appears, with anti-HBc being the only marker 1
3. Overlooking reactivation risk: Patients with resolved HBV infection (anti-HBc positive) can experience reactivation during immunosuppression 1
4. Incomplete testing: Testing only for HBsAg and anti-HBc without anti-HBs may miss important information about immunity status 1

Remember that the complete serologic profile (HBsAg, anti-HBc, and anti-HBs) provides the most accurate assessment of HBV status and should guide appropriate management decisions.