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

Interpretation of Hepatitis B Surface Antigen Qualitative Reaction

A positive Hepatitis B surface antigen (HBsAg) qualitative test result indicates current active HBV infection, meaning the person is infected with the hepatitis B virus and is considered infectious. 1

What HBsAg Positivity Means

• HBsAg is the hallmark serological marker for hepatitis B virus (HBV) infection and is the first marker to appear in acute infection, typically detectable 1-10 weeks before symptom onset 1
• A positive HBsAg test confirms the diagnosis of current HBV infection, which could be either acute or chronic 1, 2
• All individuals with positive HBsAg are considered infectious and capable of transmitting the virus through blood, body fluids, or sexual contact 1, 2
• If HBsAg persists for more than 6 months, the infection is considered chronic rather than acute 1

Interpreting HBsAg Results in Context

HBsAg results should be interpreted alongside other serological markers for complete understanding of infection status:

• HBsAg positive + Total anti-HBc positive + IgM anti-HBc positive = Acute HBV infection 3, 1
• HBsAg positive + Total anti-HBc positive + IgM anti-HBc negative = Chronic HBV infection 3, 1
• HBsAg positive + Total anti-HBc negative = Early acute infection; can also be transiently positive (up to 18 days) after vaccination 3
• HBsAg negative + Total anti-HBc positive + Anti-HBs positive = Resolved HBV infection with immunity 3, 4
• HBsAg negative + Anti-HBc negative + Anti-HBs positive = Immunity from vaccination 3, 4
• HBsAg negative + Anti-HBc negative + Anti-HBs negative = Never infected, susceptible to infection 3, 1

Clinical Implications of Positive HBsAg

• All patients who test positive for HBsAg should undergo a complete evaluation to determine the activity and severity of the infection 5
• Assessment should include:
  • Tests of disease activity (AST, ALT) 5
  • Tests of liver function (bilirubin, albumin, prothrombin time) 5
  • Tests of viral replication status (HBeAg, anti-HBe, HBV DNA titer) 5
  • Screening for coinfection with other viruses (HIV, HCV, HDV) in high-risk individuals 2
• Ultrasound is recommended to assess for signs of cirrhosis and to exclude focal lesions in the liver 5
• Liver biopsy or non-invasive fibrosis assessment may be recommended in patients with abnormal liver enzymes 2, 5

Management Considerations

• Treatment decisions are based on multiple factors including:
  • HBV DNA levels and ALT elevation 2
  • HBeAg status 2
  • Presence of significant fibrosis or cirrhosis 2
  • Age and family history of hepatocellular carcinoma (HCC) 2
• Regular monitoring of liver function tests and HBV DNA levels is necessary 2
• Surveillance for HCC with ultrasound every 6 months is recommended for high-risk patients 2
• Patients should be counseled on preventing transmission by practicing safe sex, avoiding sharing personal items, and not donating blood or organs 2

Special Considerations

• Occult HBV infection can occur when HBsAg is undetectable despite the presence of HBV DNA 1
• Transient HBsAg positivity can occur up to 18 days following vaccination (up to 52 days in hemodialysis patients) and is clinically insignificant 1
• Quantitative HBsAg assays are increasingly being used to monitor viral replication and predict treatment outcomes 6, 7, 8
• Rapid diagnostic tests for HBsAg detection have shown excellent specificity (98.0-99.5%) and sensitivity (98.3-99.3%) compared to standard immunoassays 9

Common Pitfalls to Avoid

• Not screening high-risk individuals for HBV coinfections (HIV, HCV, HDV) 2
• Missing the opportunity to screen and vaccinate close contacts of HBsAg-positive individuals 2
• Inadequate monitoring for HCC in high-risk patients 2
• Not recognizing the risk of HBV reactivation in patients receiving immunosuppressive therapy 2