What is the recommended test for screening active Hepatitis B (HB)?

Screening for Active Hepatitis B Infection

The recommended test for screening active hepatitis B infection is the hepatitis B surface antigen (HBsAg) test, which should be performed using an FDA-licensed or FDA-approved test with confirmatory testing for initially reactive results. 1

Primary Screening Test

HBsAg testing is the cornerstone of hepatitis B screening and is used to identify active infection. A positive HBsAg result indicates the presence of active hepatitis B virus (HBV) infection, which could be either acute or chronic.

• HBsAg tests have excellent performance characteristics:
  • Sensitivity >98% 2
  • Specificity 98-99.5% 2
  • Modern immunoassays can detect HBsAg at concentrations as low as 0.5-0.7 ng/ml 3

Confirmatory and Additional Testing

When an HBsAg test is initially reactive, the following steps should be taken:

1. Confirmatory testing: A licensed, neutralizing confirmatory test should be performed on initially reactive specimens 1

2. Differentiation between acute and chronic infection:

   • If HBsAg is positive, testing for IgM anti-HBc (hepatitis B core antibody) helps distinguish between acute and chronic infection 1
   • Acute HBV infection is characterized by the presence of HBsAg followed by IgM anti-HBc 1
   • Chronic infection is confirmed by the persistence of HBsAg for at least 6 months or the absence of IgM anti-HBc 1

3. Additional serological markers that may be useful:

   • Anti-HBs (hepatitis B surface antibody) - indicates immunity from vaccination or recovery from infection
   • Total anti-HBc - indicates previous or ongoing infection
   • HBeAg (hepatitis B e antigen) - indicates high viral replication and infectivity 1

Testing in Special Populations

Certain populations should be prioritized for HBsAg screening:

• Persons born in regions with HBsAg prevalence >2% (parts of Eastern Europe, Asia, Africa, Middle East, Pacific Islands) 1
• Men who have sex with men (MSM) and injection drug users 1
• Persons receiving cytotoxic or immunosuppressive therapy 1, 4
• Persons with persistently elevated liver enzymes (ALT/AST) of unknown etiology 1
• Pregnant women 1
• Household contacts and sexual partners of HBV-infected individuals 1
• Hemodialysis patients 1
• HIV-positive individuals 1

Testing Methods and Formats

Several testing formats are available for HBsAg detection:

• Laboratory-based enzyme immunoassays (EIAs) - gold standard with high sensitivity and specificity 3
• Rapid diagnostic tests (RDTs) - useful in resource-limited settings or for point-of-care testing, with specificity of 98-99.5% and sensitivity of 98.3-99.3% 2
• Immunochromatographic assays - provide rapid results with good accuracy (sensitivity 95%, specificity 100%) 5

Clinical Considerations

• A single HBsAg test is sufficient for initial screening in most cases 6
• Aspartate aminotransferase (AST) levels correlate well with histological hepatitis activity in HBsAg-positive individuals 6
• False-negative HBsAg results may occur in:
  • Inactive HBsAg carriers
  • Patients on nucleoside/nucleotide analogue treatment 2
  • Early window period of infection

Common Pitfalls to Avoid

• Relying solely on liver enzyme tests without HBsAg testing
• Failing to perform confirmatory testing for initially reactive HBsAg results
• Not testing high-risk individuals regardless of vaccination history
• Overlooking the need for comprehensive serological testing (HBsAg, anti-HBc, anti-HBs) in immunocompromised patients 4
• Misinterpreting isolated anti-HBc positivity, which may indicate occult HBV infection, especially in immunocompromised patients 4

By following these evidence-based recommendations for HBsAg testing, clinicians can effectively screen for active hepatitis B infection, leading to appropriate management and reduced morbidity and mortality from HBV-related complications.