If anti‑HBs (hepatitis B surface antibody) is positive, does that indicate an active hepatitis B infection?

No, Anti-HBs Positivity Indicates Immunity, NOT Active Infection

A positive anti-HBs (hepatitis B surface antibody) test indicates immunity from either past resolved infection or vaccination—it does NOT indicate active hepatitis B infection. 1

Understanding the Serologic Pattern

Anti-HBs represents the protective antibody response that develops:

• After recovery from HBV infection (typically appearing 3-4 months after HBsAg clearance)
• After successful vaccination (the only HBV marker present post-vaccination)
• Following HBIG administration (temporary, lasting 4-6 months) 2, 3

Key Distinction: Active Infection vs. Immunity

Active HBV infection is indicated by:

• HBsAg positivity (hepatitis B surface antigen)—this is the marker of active infection, whether acute or chronic 1
• IgM anti-HBc for acute/recent infection
• Detectable HBV DNA

Immunity is indicated by:

• Anti-HBs positivity with HBsAg negativity
• Anti-HBs ≥10 mIU/mL is considered protective 1, 3

Critical Serologic Interpretation

According to the CDC's interpretation table 1:

HBsAg	Anti-HBc	Anti-HBs	Interpretation
Negative	Positive	Positive	Recovered from past infection and immune
Negative	Negative	Positive	Immune from vaccination
Positive	Positive	Negative	Chronic infection (active)
Positive	Positive (IgM+)	Negative	Acute infection (active)

Important Clinical Caveats

Rare exceptions where both HBsAg and anti-HBs can coexist:

• This paradoxical pattern is extremely rare and may indicate:
  • Immune escape variants with ongoing viral replication 4, 5
  • Complex immune dysfunction
  • Often associated with advanced liver disease and high viral loads 5
  • These patients still have active infection despite anti-HBs presence

Passively acquired anti-HBs does NOT confer immunity:

• Recent HBIG administration 2, 3
• Recent blood product transfusion 6
• These scenarios show anti-HBs positivity without true protective immunity

Clinical Algorithm

When you see anti-HBs positive:

1. Check HBsAg status first

   • If HBsAg negative → Patient is immune (either from past infection or vaccination)
   • If HBsAg positive → Rare paradoxical pattern; active infection with immune escape

2. Check anti-HBc to distinguish source of immunity

   • Anti-HBc negative → Immunity from vaccination only
   • Anti-HBc positive → Immunity from past natural infection

3. Verify no recent passive antibody transfer

   • Recent HBIG or blood products can cause false reassurance

Bottom line: Isolated anti-HBs positivity (with negative HBsAg) definitively indicates immunity and protection against HBV infection, not active disease. The presence of HBsAg—not the absence of anti-HBs—is what defines active infection. 1, 2, 1, 3