Interpretation of Qualitative Hepatitis B Surface Antibody Test Results
A qualitative (QL) hepatitis B surface antibody (anti-HBs) test indicates whether a person has immunity to hepatitis B virus (HBV) infection, either through vaccination or recovery from natural infection. 1, 2
Understanding Anti-HBs Results
A qualitative anti-HBs test provides a simple positive or negative result:
- Positive result: Indicates the presence of protective antibodies at levels ≥10 mIU/mL, which is considered protective against HBV infection 1, 2
- Negative result: Indicates absence of protective antibodies or levels below the protective threshold
Clinical Significance
The interpretation of a qualitative anti-HBs result depends on other hepatitis B serological markers:
| Anti-HBs | Anti-HBc | HBsAg | Interpretation |
|---|---|---|---|
| Positive | Negative | Negative | Immunity through vaccination |
| Positive | Positive | Negative | Immunity due to resolved natural infection |
| Negative | Positive | Positive | Chronic hepatitis B infection |
| Negative | Negative | Negative | Susceptible to HBV infection |
Important Considerations
Vaccination vs. Natural Immunity: A positive anti-HBs with negative anti-HBc indicates vaccine-derived immunity, while positive anti-HBs with positive anti-HBc indicates immunity from resolved natural infection 1
Protective Threshold: Current commercially available assays consider anti-HBs levels ≥10 mIU/mL as protective 1, 2
Potential False Positives: Anti-HBs can be detected for several months after hepatitis B immune globulin (HBIG) administration, which represents passive immunity rather than active immunity 1
Window Period: During acute HBV infection recovery, there may be a "window period" when HBsAg has disappeared but anti-HBs is not yet detectable; during this time, HBc IgM antibody can confirm recent infection 1
Clinical Applications
Post-vaccination Testing: Qualitative anti-HBs testing can confirm successful immunization
Immunity Assessment: Determines if a person is protected against HBV infection
Monitoring High-Risk Groups: Healthcare workers, hemodialysis patients, and immunocompromised individuals may require periodic monitoring of anti-HBs levels 2
Pitfalls to Avoid
Recent HBIG Administration: Can cause transiently positive anti-HBs that does not reflect true immunity 1, 3
Isolated Anti-HBc: When anti-HBs is negative but anti-HBc is positive, this may represent:
- Previous infection with waning anti-HBs levels
- False-positive anti-HBc (especially in low-prevalence populations)
- "Window period" of acute infection 1
Rare Coexistence of HBsAg and Anti-HBs: In some chronic HBV infections, both markers can coexist, which may be associated with viral mutations and progressive liver disease 4
For accurate clinical interpretation, qualitative anti-HBs results should always be considered alongside other hepatitis B serological markers, particularly HBsAg and anti-HBc.