Is a patient who is hepatitis B surface antigen positive with negative hepatitis B core antibody (both IgM and total) indicative of a past infection or vaccination?

HBsAg Positive with Negative Core Antibodies: Early Acute Infection

This serologic pattern (HBsAg positive, anti-HBc IgM negative, total anti-HBc negative) indicates early acute hepatitis B infection, not past infection or vaccination. 1

Why This is NOT Vaccination

• Vaccination produces anti-HBs antibodies WITHOUT any other markers—specifically, vaccinated individuals are anti-HBs positive and anti-HBc negative, never HBsAg positive 1
• The presence of HBsAg always indicates current HBV infection (either acute or chronic), and all HBsAg-positive persons are infectious 1
• Vaccine recipients can only show transient HBsAg positivity for up to 18 days post-vaccination (up to 52 days in hemodialysis patients), which is clinically insignificant and would not persist 1

Why This is NOT Past Infection

• Past resolved infection shows a completely different pattern: HBsAg negative, anti-HBs positive, and total anti-HBc positive 1
• Persons who recover from HBV infection eliminate HBsAg from the blood and develop anti-HBs, typically within 3-4 months 1
• The presence of HBsAg definitively rules out resolved past infection 1

Understanding the Timeline of Acute Infection

This specific serologic pattern represents the very earliest phase of acute HBV infection:

• HBV DNA becomes detectable first, before HBsAg appears 1
• HBsAg appears 1-10 weeks after exposure 1
• Anti-HBc (both IgM and IgG) appears 1-2 weeks AFTER HBsAg becomes detectable 1
• Your patient is in this narrow window where HBsAg has appeared but anti-HBc has not yet developed 1

Critical Next Steps

Immediate actions required:

• Repeat complete hepatitis B panel in 1-2 weeks to confirm acute infection and monitor for development of anti-HBc IgM 1
• Obtain HBV DNA level to confirm active viral replication 1
• Check liver function tests (ALT/AST) to assess hepatic injury 1
• The patient is highly infectious—counsel on transmission prevention immediately 1
• Identify and vaccinate all sexual and household contacts 1

Important Caveat About False Positives

• Isolated HBsAg positivity can rarely represent a false-positive result due to heterophilic antibody interference 2
• However, given the clinical context, treat this as true acute infection until proven otherwise with repeat testing and HBV DNA measurement 1, 2
• If HBsAg persists beyond 6 months, the infection is deemed chronic rather than acute 1