What is Anti-HBs (Antibody to Hepatitis B surface antigen) for?

What is Anti-HBs (Antibody to Hepatitis B Surface Antigen) For?

Anti-HBs is the antibody that indicates immunity to hepatitis B virus, either from successful vaccination or recovery from past infection, and is the only HBV antibody marker present after vaccination. 1

Primary Functions of Anti-HBs

Immunity Indicator

• Anti-HBs demonstrates protective immunity against hepatitis B infection when present at levels ≥10 mIU/mL. 2
• This antibody is produced after a resolved HBV infection or following successful hepatitis B vaccination. 1
• The presence of anti-HBs without other HBV markers (negative HBsAg and negative anti-HBc) specifically indicates vaccine-derived immunity. 3

Distinguishing Infection Status

• Anti-HBs helps differentiate between various HBV infection states when interpreted alongside other serologic markers. 1
• When anti-HBs is positive with anti-HBc positive (and HBsAg negative), this indicates recovery from past natural infection with resulting immunity. 1
• When anti-HBs is the only positive marker, this confirms immunity from vaccination alone without prior natural infection. 1

Clinical Applications

Vaccination Response Assessment

• Testing for anti-HBs 1-2 months after completing the hepatitis B vaccine series confirms adequate immune response. 4
• Healthcare workers should be tested for anti-HBs upon hire if they have documented hepatitis B vaccination history. 4
• Those with anti-HBs <10 mIU/mL should receive additional vaccine doses to achieve protective immunity. 4

Risk Stratification for Immunosuppression

• Individuals with vaccine-derived immunity (anti-HBs positive, anti-HBc negative) have minimal risk of HBV reactivation during immunosuppressive therapy because they lack prior natural infection. 3
• In contrast, patients who are anti-HBc positive but anti-HBs negative face up to 68.3% risk of HBV reactivation with certain immunosuppressive regimens like rituximab-based chemotherapy. 5
• This distinction is critical for determining who requires antiviral prophylaxis before starting immunosuppression. 5

Monitoring Special Populations

• Dialysis patients may require annual anti-HBs screening even if previously immune, to monitor for potential loss of immunity. 5
• Healthcare personnel with ongoing HBV exposure risk require periodic anti-HBs testing. 5
• No further routine testing is typically required in immunocompetent individuals with positive anti-HBs, though high-risk settings like dialysis units may warrant annual screening. 3

Important Clinical Caveats

Immunologic Memory vs. Antibody Levels

• Even when anti-HBs levels decline below 10 mIU/mL years after vaccination, immunologic memory typically persists and provides ongoing protection. 6
• Memory B lymphocytes capable of producing anti-HBs remain present even as circulating antibody levels fall. 6
• Booster vaccination in healthy vaccinees who lose detectable antibody produces large, rapid increases in anti-HBs, demonstrating intact memory. 6
• Routine booster vaccination is generally unnecessary within 5-12 years after primary vaccination series in healthy individuals. 6

Passive vs. Active Immunity

• Passively acquired anti-HBs (from hepatitis B immune globulin or recent transfusion) does not confer lasting immunity and can create false reassurance. 7
• Patients who receive blood products may have detectable anti-HBs that does not represent true immune protection. 7
• When anti-HBs is acquired passively, susceptibility to infection returns as the antibody declines. 6

Limitations in Certain Contexts

• Different laboratory assays may have varying cutoff values for anti-HBs detection. 4
• In individuals with frequent HBV exposure (such as healthcare workers with blood contact), anti-HBs is more likely to identify prior immunity compared to those with infrequent exposures. 8
• The protective level of anti-HBs is generally considered ≥10 mIU/mL, though some individuals maintain protection at lower detectable levels. 2

Role in Hepatitis B Prevention Strategy

Public Health Significance

• The hepatitis B vaccine is recognized as the first anti-cancer vaccine because anti-HBs immunity prevents primary liver cancer (hepatocellular carcinoma). 2
• Universal childhood immunization producing anti-HBs has decreased hepatocellular carcinoma incidence in children and adults. 2
• Anti-HBs is the cornerstone marker for evaluating the success of vaccination programs aimed at eliminating HBV transmission. 1