What Does Hepatitis B Surface Antibody (Anti-HBs) Mean?
A positive hepatitis B surface antibody (anti-HBs) result indicates protective immunity against hepatitis B virus infection, achieved either through successful vaccination or recovery from a past natural HBV infection. 1, 2
Defining Protective Immunity
- Anti-HBs levels ≥10 mIU/mL are considered protective, providing >90% protection against both acute hepatitis B disease and chronic HBV infection in immunocompetent individuals. 3
- This threshold is uniformly recognized by the CDC and international guidelines as the standard for protective immunity. 3
Two Distinct Sources of Anti-HBs
Vaccine-Derived Immunity
- When anti-HBs is positive AND anti-HBc (hepatitis B core antibody) is negative, this indicates immunity from vaccination, not natural infection. 1, 2
- These individuals have never been infected with HBV but are protected through immunization. 1
Natural Infection-Derived Immunity
- When anti-HBs is positive AND anti-HBc is also positive, this indicates recovery from a past natural HBV infection with acquired immunity. 1, 2
- These individuals cleared the infection and developed natural immunity. 1
Long-Term Protection and Immune Memory
- Immunocompetent persons who achieve anti-HBs ≥10 mIU/mL maintain lifelong protection through immune memory, even when antibody levels subsequently decline below 10 mIU/mL. 3
- Protection persists for at least 30 years among vaccine responders, and likely for life, through B and T lymphocyte memory cells rather than circulating antibody alone. 3
- 15-50% of vaccinated individuals will have anti-HBs levels decline to <10 mIU/mL within 5-15 years, yet they remain protected against clinically significant infection. 3
- 88% of vaccinated individuals mount an anamnestic response when given a challenge dose 30 years after initial vaccination, demonstrating persistent immune memory. 3
Clinical Implications
For Immunocompetent Individuals
- Persons with documented anti-HBs ≥10 mIU/mL do not require routine booster doses or periodic retesting. 3, 2
- They are not infectious and cannot transmit HBV to others. 2
- No further HBV vaccination is needed. 2
For Special Populations Requiring Different Management
Annual anti-HBs testing with booster doses when levels fall <10 mIU/mL is recommended for: 3, 2
- Hemodialysis patients
- HIV-infected persons
- Hematopoietic stem-cell transplant recipients
- Persons receiving chemotherapy
- Other immunocompromised patients
Post-vaccination testing (1-2 months after final dose) is specifically recommended for: 3
- Healthcare workers (to document immunity before occupational exposure)
- Infants born to HBsAg-positive mothers
- Sexual partners of HBsAg-positive persons
- Public safety workers at risk for blood/body fluid exposure
Important Caveats and Pitfalls
Passively Acquired Anti-HBs
- Anti-HBs can be detected for 4-6 months following hepatitis B immune globulin (HBIG) administration, which does not indicate true immunity. 1
- Intravenous immunoglobulin can produce passive transfer of anti-HBs, leading to false interpretation of immune status. 3, 4
- This is particularly important in recently transfused patients, where passively acquired anti-HBs may not confer actual protection. 4
Transient Post-Vaccination Positivity
- Transient HBsAg positivity can occur up to 18 days following vaccination (up to 52 days among hemodialysis patients) and is clinically insignificant. 1, 3
Low-Level Anti-HBs Results
- Anti-HBs levels between 1-9 mIU/mL indicate measurable but subprotective antibody response. 3
- Low-positive test results for anti-HBs should be interpreted with caution, as they may be nonspecific and do not persist in many cases. 5
- For levels <10 mIU/mL, administer a single booster dose and retest 1-2 months later to determine if additional doses are needed. 3
Isolated Anti-HBc Positivity
- When only anti-HBc is positive (without anti-HBs or HBsAg), this can indicate past infection with loss of anti-HBs, or in rare cases, occult chronic infection. 1
- These persons are unlikely to be infectious except under circumstances involving direct percutaneous exposure to large quantities of blood. 1