Hepatitis B Serology Interpretation: Isolated Anti-HBs Positivity
This serological pattern (HBsAg negative, anti-HBc negative, anti-HBs positive, with all other markers negative) indicates immunity from hepatitis B vaccination (Answer C: Immunization). 1
Definitive Serological Pattern Analysis
The CDC's Advisory Committee on Immunization Practices provides explicit guidance for this exact serological profile:
Isolated anti-HBs positivity (negative HBsAg, negative anti-HBc, positive anti-HBs) indicates vaccine-induced immunity when anti-HBs concentration is ≥10 mIU/mL after vaccine series completion. 1
This pattern definitively distinguishes vaccination-induced immunity from natural infection, as persons who recover from natural HBV infection are typically positive for both anti-HBs and anti-HBc, whereas persons who respond to hepatitis B vaccine are positive only for anti-HBs. 1
Why Other Answer Choices Are Incorrect
Active infection (Answer A) is ruled out because:
- HBsAg would be positive in any active infection (acute or chronic). 1
- All HBsAg-positive persons are infectious, and this patient is HBsAg negative. 1
Chronic infection (Answer B) is ruled out because:
- Chronic infection requires HBsAg positivity persisting for >6 months. 1
- The serological pattern would show HBsAg positive, total anti-HBc positive, IgM anti-HBc negative. 1
Past infection (Answer D) is ruled out because:
- Resolved past infection with natural immunity shows HBsAg negative, anti-HBc positive, anti-HBs positive, and HBV DNA negative. 1, 2
- The critical distinguishing feature is that anti-HBc would be positive in past infection, not negative as in this case. 1
Clinical Pearls and Important Caveats
Protective immunity threshold:
- Anti-HBs concentration ≥10 mIU/mL indicates protection against HBV infection. 1, 2
- This threshold should be confirmed, especially in immunocompromised patients or those with chronic liver disease who may have lower seroconversion rates. 3
Potential pitfalls to consider:
- Transient HBsAg positivity can occur up to 18 days following vaccination (up to 52 days in hemodialysis patients) and is clinically insignificant. 1
- Passively acquired anti-HBs from hepatitis B immune globulin (HBIG) administration can be detected for 4-6 months and does not represent true immunity. 1, 4
- If the patient received HBIG or blood products recently, the anti-HBs may be passively transferred rather than vaccine-induced, though this would still not represent active or past infection. 1
When to retest:
- In patients with chronic liver disease or immunosuppression undergoing vaccination, postvaccination testing is recommended to confirm adequate seroconversion. 3
- If anti-HBs levels are suboptimal or the patient has risk factors for exposure, consider repeat vaccination using standard or accelerated schedules. 3