How should I interpret a hepatitis B serology pattern of positive hepatitis B surface antigen (HBsAg), positive hepatitis B surface antibody (anti‑HBs), and non‑reactive hepatitis B core antibody (anti‑HBc) in a patient who was vaccinated nine years ago?

Interpretation of Hepatitis B Serology Pattern

This serological pattern (HBsAg-positive, anti-HBs-positive, anti-HBc-negative) is highly unusual and most likely represents either a false-positive HBsAg result, laboratory error, or sample contamination rather than true hepatitis B infection. 1, 2, 3

Immediate Action Required

Order confirmatory testing immediately with the following specific tests 4:

• Repeat HBsAg testing using a different commercial assay or neutralization test
• Quantitative HBV DNA (PCR testing)
• Repeat anti-HBc testing (both total and IgM)
• Quantitative anti-HBs level to verify the titer

Why This Pattern is Problematic

The combination of positive HBsAg with absent anti-HBc contradicts the natural history of hepatitis B infection 4:

• Anti-HBc appears at the onset of acute infection and persists for life in all persons with true HBV infection 4
• Patients who respond to vaccination develop anti-HBs but remain anti-HBc negative (since anti-HBc only emerges after actual HBV infection) 4
• The presence of both HBsAg and anti-HBs simultaneously with negative anti-HBc has no recognized place in the natural history of HBV infection 4

Most Likely Explanations

1. False-Positive HBsAg (Most Common)

Heterophilic antibody interference can cause isolated false-positive HBsAg results 1, 2:

• This occurs in 0.05-1.3% of routine testing 3
• The patient's vaccination history 9 years ago supports this being a false positive
• True HBV infection would show anti-HBc positivity 4

2. Laboratory Error or Sample Contamination

Sample mix-up or contamination must be excluded 3:

• Repeat testing with a fresh sample is essential
• Use a different testing platform if available 1

3. Very Early Acute Infection (Extremely Unlikely)

The window period of acute HBV infection could theoretically show HBsAg before anti-HBc appears 3:

• However, this occurs within the first 3-5 weeks of infection 4
• The presence of anti-HBs makes this scenario virtually impossible
• Anti-HBs does not develop during acute infection 4

Definitive Interpretation Based on Confirmatory Testing

If HBV DNA is Undetectable:

This confirms a false-positive HBsAg result 4:

• The patient has vaccine-induced immunity (anti-HBs positive from vaccination 9 years ago)
• No HBV infection exists
• No further hepatitis B-related action needed

If HBV DNA is Detectable:

This would represent an extraordinarily rare scenario requiring immediate hepatology referral 4:

• Consider occult hepatitis B infection with unusual serological pattern
• Evaluate for immunocompromised state
• Assess liver function tests (AST/ALT) 4

Common Pitfalls to Avoid

• Do not assume chronic HBV infection based on isolated HBsAg positivity without anti-HBc 2, 3
• Do not initiate antiviral therapy before confirmatory testing 4
• Do not perform unnecessary contact tracing until true infection is confirmed 4
• Do not delay confirmatory testing - this should be done within days, not weeks 3

Expected Outcome

In >70% of cases with this serological pattern, confirmatory testing excludes HBV infection 3. Given the patient's vaccination history and the absence of anti-HBc, the overwhelming likelihood is that this represents a false-positive HBsAg result with true vaccine-induced immunity 4, 1.