Primary Lab Test for Hepatitis B Immunity
The primary lab test for hepatitis B immunity is antibody to hepatitis B surface antigen (anti-HBs), with a protective level defined as ≥10 mIU/mL. 1
Understanding Anti-HBs Testing
Anti-HBs is the definitive marker of immunity to hepatitis B virus (HBV), whether acquired through vaccination or recovery from natural infection. 1 The presence of anti-HBs at concentrations ≥10 mIU/mL indicates protective immunity and is the standard threshold established by vaccine efficacy studies. 1, 2
Key Distinctions in Immunity Patterns
Vaccine-induced immunity shows positive anti-HBs with negative anti-HBc (hepatitis B core antibody), indicating the person has never been infected but has developed antibodies from vaccination. 1
Natural immunity from resolved infection shows positive anti-HBs with positive anti-HBc, indicating the person recovered from a previous HBV infection and now has protective antibodies. 1
Immunocompetent persons with anti-HBs ≥10 mIU/mL after completing the primary vaccine series have long-term protection and do not need periodic retesting. 1, 2
When to Perform Post-Vaccination Testing
Postvaccination serologic testing for anti-HBs should be performed 1-2 months after administration of the final vaccine dose using a quantitative method that allows detection of the protective concentration (≥10 mIU/mL). 1, 2
Specific Populations Requiring Post-Vaccination Testing
Healthcare personnel and public safety workers with risk for blood or body fluid exposure require testing to document immunity and determine need for revaccination if non-responsive. 1
Hemodialysis patients need post-vaccination testing followed by annual monitoring, as they have lower seroconversion rates and may require booster doses when levels fall below 10 mIU/mL. 1, 2
Immunocompromised persons (including HIV-infected persons, hematopoietic stem-cell transplant recipients, and those receiving chemotherapy) require testing to determine need for revaccination and may need annual anti-HBs concentration assessment. 1, 2
Sex partners of HBsAg-positive persons should be tested to determine need for revaccination and other protective measures. 1
Qualitative vs. Quantitative Testing
For routine clinical practice, qualitative anti-HBs testing is sufficient and more cost-effective for the vast majority of patients, providing a binary positive/negative result with the ≥10 mIU/mL threshold. 2
- Quantitative anti-HBs testing measures exact antibody concentrations and is specifically indicated for monitoring hepatitis B immunoglobulin (HBIG) therapy adequacy in liver transplant recipients and for annual monitoring in hemodialysis patients. 2
Management of Non-Responders
Persons with anti-HBs <10 mIU/mL after the primary vaccine series should be revaccinated with a complete second series, followed by anti-HBs testing 1-2 months after the final dose. 1
After revaccination, persons who still do not achieve protective anti-HBs levels should be tested for HBsAg to rule out chronic infection as the cause of non-response. 1
If HBsAg-positive, the person requires appropriate management for chronic HBV infection, and household, sexual, and needle-sharing contacts should be identified and vaccinated. 1
Critical Clinical Pitfalls
Do not confuse anti-HBs testing with HBsAg testing—anti-HBs indicates immunity or recovery, while HBsAg indicates active infection. 2 This is a common error that can lead to serious mismanagement.
Anti-HBs can be detected for several months after hepatitis B immune globulin (HBIG) administration, representing passively acquired antibody rather than true immunity. 1, 3 In patients recently transfused with blood products or given HBIG, anti-HBs may not signify protective immunity and should be interpreted with caution. 3
The 10 mIU/mL threshold represents the minimum protective level established by vaccine studies and should not be interpreted as a gray zone—levels at or above this threshold confer protection against all HBV genotypes. 1, 2