What does a positive Hepatitis B surface antigen (HBsAg) result mean?

What Does a Positive HBsAg Mean?

A positive HBsAg result indicates active hepatitis B virus (HBV) infection—either acute or chronic—and the person should be considered infectious. 1

Determining Acute vs. Chronic Infection

The critical next step is distinguishing between acute and chronic infection using additional serologic markers:

• Acute infection is confirmed by the presence of IgM anti-HBc (immunoglobulin M antibody to hepatitis B core antigen), which appears at symptom onset and persists for up to 6 months if the infection resolves 1, 2
• Chronic infection is confirmed by either the absence of IgM anti-HBc OR the persistence of HBsAg for at least 6 months 1, 3
• All HBsAg-positive persons must be considered infectious regardless of whether the infection is acute or chronic 1, 3

Complete Serologic Interpretation

The full clinical picture requires a complete serologic panel:

• HBsAg (+), IgM anti-HBc (+), anti-HBs (−) = Acute hepatitis B 1, 2
• HBsAg (+), total anti-HBc (+), IgM anti-HBc (−) = Chronic hepatitis B 1, 2, 4
• HBsAg (+), all other markers (−) = Early acute infection (first 3-5 weeks) or transient positivity up to 18 days after vaccination 1

Immediate Clinical Actions for HBsAg-Positive Patients

For Suspected Acute Infection:

• Order IgM anti-HBc to confirm acute infection (only in patients with clinical evidence of acute hepatitis or epidemiologic link to HBV) 1, 2
• Provide supportive care—no specific antiviral treatment exists for acute hepatitis B 2
• Monitor for progression to acute liver failure (occurs in ~1% of cases) 2
• Screen and vaccinate close contacts immediately 2, 3

For Chronic Infection:

• Refer to a specialist experienced in managing chronic liver disease 1, 3
• Complete initial evaluation including: HBV DNA levels, ALT levels, HBeAg status, and assessment of liver fibrosis (via transient elastography or biopsy) 3
• Screen for coinfections (HIV, HCV, HDV) in high-risk individuals 3
• Initiate hepatocellular carcinoma (HCC) surveillance with baseline ultrasound for all HBsAg-positive persons ≥20 years old 3
• Continue HCC surveillance every 6 months in high-risk patients (cirrhosis, family history of HCC, older age) 3

Transmission Prevention Counseling

Counsel all HBsAg-positive patients on preventing transmission:

• Practice safe sex and avoid sharing needles, razors, or toothbrushes 3
• Cover open wounds 3
• Do not donate blood, organs, or tissue 3
• Screen and vaccinate all susceptible household members and sexual contacts 3

Critical Pitfalls to Avoid

• Do not test IgM anti-HBc in asymptomatic persons—the positive predictive value is low and can lead to false-positive results 1, 2, 4
• Do not miss the window to screen and vaccinate close contacts 2, 3
• Do not fail to recognize HBV reactivation risk in patients requiring immunosuppressive therapy—these patients need careful monitoring and possibly antiviral prophylaxis 3, 4
• Do not neglect HCC surveillance in high-risk patients—HBV DNA levels >10^5 copies/mL significantly increase cirrhosis and HCC risk 3
• Remember that transient HBsAg positivity can occur up to 18 days after hepatitis B vaccination and is clinically insignificant 1