What does a reactive Hepatitis B (HB) surface antibody (HBsAb) test result indicate?

Interpretation of Reactive Hepatitis B Surface Antibody (HBsAb)

A reactive Hepatitis B surface antibody (HBsAb) test indicates immunity to Hepatitis B virus (HBV) infection, either from successful vaccination or recovery from a past HBV infection. 1

Understanding HBsAb Reactivity

Reactive HBsAb can indicate two distinct scenarios:

1. Vaccine-induced immunity:

   • Pattern: HBsAb positive + HBsAg negative + HBcAb negative
   • Interpretation: Successful vaccination with no evidence of current or past infection 1

2. Natural immunity from past infection:

   • Pattern: HBsAb positive + HBsAg negative + HBcAb positive
   • Interpretation: Recovery from past HBV infection with natural immunity 1

Protection Level and Duration

• Anti-HBs levels ≥10 mIU/mL are generally considered protective against HBV infection 1
• Immunity characteristics:
  • Vaccine-induced immunity may wane over time, but memory B cells typically provide ongoing protection
  • Natural immunity from past infection usually provides lifelong protection 1

Important Considerations

False Positive Possibilities

• Passively acquired antibodies from recent hepatitis B immune globulin (HBIG) administration can cause a false positive result for up to 4-6 months 1, 2
• Recent transfusion of blood products containing HBsAb can lead to passively acquired antibodies that do not confer true immunity 2

Clinical Implications

• No HBV vaccination is needed for individuals with either natural immunity or vaccine-induced immunity 1
• No routine HBV screening is required for immune individuals unless they become immunocompromised 1

Risk of HBV Reactivation

• Individuals with natural immunity (HBsAb+/HBcAb+) are at risk of reactivation if immunosuppressed, particularly with:

  • Anti-CD20 monoclonal antibodies
  • Stem cell transplantation
  • High-dose corticosteroids
  • TNF inhibitors 1

• Individuals with vaccine-induced immunity have no risk of reactivation as there is no latent virus 1

Follow-up Recommendations

• For patients with vaccine-induced immunity:

  • No routine monitoring needed in healthy individuals
  • Annual screening with anti-HBs may be considered in certain high-risk groups 1

• For patients with natural immunity (HBsAb+/HBcAb+):

  • No further testing required in immunocompetent individuals
  • Consider prophylactic antiviral therapy if undergoing immunosuppressive therapy 1

Pitfalls to Avoid

• Do not assume immunity without confirming the complete serologic pattern (HBsAb, HBsAg, HBcAb) 1
• Be cautious in interpreting isolated HBsAb positivity in recently transfused patients 2
• Remember that quantitative anti-HBs levels provide valuable information, as higher titers offer better protection against reactivation 1

In summary, a reactive HBsAb test generally indicates protection against HBV infection, but the complete serologic profile should be evaluated to determine whether this immunity is from vaccination or past infection, as this distinction has important clinical implications for monitoring and management, especially in immunocompromised states.