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Here is a comprehensive summary of Total Anti-HBs Antibody (Anti-HBs Ab):
Total Anti-HBs Ab (Antibody to Hepatitis B Surface Antigen)
What It Is
Anti-HBs is the protective antibody produced against the hepatitis B surface antigen (HBsAg). Its presence indicates either:
- Recovery from past HBV infection (appears alongside anti-HBc)
- Successful response to HBV vaccination (appears alone, without anti-HBc)
Interpretation of Levels
| Anti-HBs Level | Meaning |
|---|---|
| ≥ 10 mIU/mL | Adequate immunity — protected against HBV infection |
| < 10 mIU/mL | Insufficient immunity — non-responder or waned immunity |
| Undetectable | No protection; susceptible to HBV |
The threshold of 10 mIU/mL is the internationally accepted cut-off for seroprotection.
Clinical Significance
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Post-vaccination testing: After completing the 3-dose HBV vaccine series, 5–19% of people fail to seroconvert. Checking anti-HBs confirms adequate immune response.
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Protective role: The temporal appearance of anti-HBs with resolution of HBV infection, and protection against reinfection, confirms anti-HBs as the key neutralising antibody. — Harrison's Principles of Internal Medicine 22E
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Waning immunity: Vaccine-induced anti-HBs wanes over time, but immunological memory persists in competent responders, providing continued protection even when titers fall below 10 mIU/mL.
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Coexistence with HBsAg: In ~5–10% of chronic HBV patients, low-level, low-affinity anti-HBs can co-exist with HBsAg — this does not indicate clearance, and may be associated with higher risk of fibrosis/cirrhosis. — Harrison's 22E
Post-Exposure Management (Based on Anti-HBs Status)
| Vaccination Status | Anti-HBs Level | Action |
|---|---|---|
| Vaccinated, known responder | ≥ 10 mIU/mL | No action needed |
| Vaccinated, non-responder (1 series) | < 10 mIU/mL | HBIG × 1 + repeat vaccine series |
| Vaccinated, non-responder (2 series) | < 10 mIU/mL | HBIG × 2 (1 month apart) |
| Unknown vaccination response | Unknown | Test anti-HBs; treat based on result |
— Current Surgical Therapy 14e; Washington Manual of Medical Therapeutics
Serological Patterns
- Anti-HBs alone (positive) → Vaccine-induced immunity
- Anti-HBs + anti-HBc (positive) → Natural infection with recovery
- Anti-HBc alone (isolated) → Remote past infection or window period
- "Window period": After HBsAg disappears but before anti-HBs appears — IgM anti-HBc may be the only detectable marker — Harrison's 22E
In summary, total anti-HBs Ab is the key marker of protective immunity to hepatitis B. A level ≥ 10 mIU/mL confirms seroprotection, while lower levels indicate the need for re-vaccination or post-exposure prophylaxis.
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