What does a positive Hepatitis B (Hep B) surface antibody (ab) test result mean?

Meaning of Positive Hepatitis B Surface Antibody (HBsAb)

A positive hepatitis B surface antibody (anti-HBs) test indicates immunity to hepatitis B virus (HBV) infection, either from successful vaccination or recovery from a past HBV infection. 1

Types of Immunity Indicated by Positive HBsAb

The meaning of a positive HBsAb result depends on other serological markers:

1. Vaccine-induced immunity:

   • Pattern: HBsAb positive + HBsAg negative + HBcAb negative
   • Interpretation: Immunity from vaccination with no evidence of current or past infection 1, 2

2. Natural immunity from past infection:

   • Pattern: HBsAb positive + HBsAg negative + HBcAb positive
   • Interpretation: Recovery from past HBV infection with natural immunity 1, 2

Protection Level and Duration

• Anti-HBs levels ≥10 mIU/mL are generally considered protective against HBV infection 2, 1
• Immunity characteristics:
  • Vaccine-induced immunity may wane over time, but memory B cells typically provide ongoing protection 1
  • Natural immunity from past infection usually provides lifelong protection 1

Special Considerations

False Positive Results

• Passively acquired antibodies from recent hepatitis B immune globulin (HBIG) administration can cause a false positive result for up to 4-6 months 1, 3
• This does not represent true immunity to HBV 3

Screening and Vaccination Recommendations

• Individuals with positive HBsAb (≥10 mIU/mL) do not need HBV vaccination 1
• For patients with vaccine-induced immunity, annual screening with anti-HBs may be recommended in certain high-risk settings (e.g., dialysis) 2
• For patients with natural immunity (HBsAb+/HBcAb+), no further testing is generally required 2, 1

Risk of HBV Reactivation

• Individuals with natural immunity (HBsAb+/HBcAb+) may be at risk of reactivation if immunosuppressed 1
• High-risk immunosuppressive regimens include:
  • Anti-CD20 monoclonal antibodies
  • Stem cell transplantation
  • High-dose corticosteroids
  • TNF inhibitors 1

Interpretation Table

HBsAg	Total anti-HBc	Anti-HBs	Interpretation	Follow-up
-	-	+	Immune due to vaccination	No vaccination needed
-	+	+	Immune due to natural infection	No vaccination needed
-	+	-	Possible interpretations: past infection with waned antibodies, "low-level" chronic infection, or false-positive anti-HBc	Consider additional testing

Clinical Implications

• Positive HBsAb generally indicates protection against future HBV infection
• For immunocompromised patients (especially those on dialysis), regular monitoring of antibody levels may be warranted 2
• In rare cases, HBsAg and anti-HBs can coexist, which may be associated with progressive liver disease 4
• For patients with chronic liver disease, screening for HBsAb is important to determine vaccination needs 5

In summary, a positive hepatitis B surface antibody test is generally good news, indicating either successful vaccination or recovery from past infection with resulting immunity to HBV.