Test to Detect Positive Hepatitis B
The hepatitis B surface antigen (HBsAg) test is the primary screening test to detect active hepatitis B infection in individuals exposed to HBV, regardless of vaccination history. 1
Primary Screening Test
- HBsAg is the single most important test because it is the only serologic marker detected during the first 3-5 weeks after infection and remains positive in all persons with chronic HBV infection. 1
- The average time from exposure to detection of HBsAg is 30 days (range: 6-60 days). 1
- HBsAg positivity indicates either acute or chronic HBV infection and requires immediate follow-up testing. 1, 2
Comprehensive Initial Testing Panel
While HBsAg is the primary test to detect infection, the Advisory Committee on Immunization Practices recommends a complete three-marker panel for comprehensive evaluation: 1
- HBsAg - detects active infection
- Anti-HBs (antibody to hepatitis B surface antigen) - detects immunity from vaccination or resolved infection
- Anti-HBc (antibody to hepatitis B core antigen) - detects past or current infection
This three-marker approach is specifically recommended for: 1
- Household, sexual, or needle-sharing contacts of HBsAg-positive persons
- Persons born in countries with HBV prevalence ≥2%
- HIV-positive persons
- Persons with elevated liver enzymes of unknown cause
- Men who have sex with men
- Current or past injection drug users
Special Testing Considerations
For dialysis patients specifically, the Centers for Disease Control and Prevention mandates testing for HBsAg, anti-HBs, and anti-HBc before admission to any outpatient dialysis facility. 1
Vaccination history does not eliminate the need for testing in high-risk populations, because persons may have been infected before vaccination or during periods when vaccination programs were not fully implemented. 1
Follow-Up Testing After Positive HBsAg
If HBsAg is positive, the following additional tests must be ordered immediately: 2
- IgM anti-HBc - distinguishes acute infection (positive) from chronic infection (negative)
- HBeAg and anti-HBe - assesses viral replication status and infectivity
- Quantitative HBV DNA - determines viral load
- Liver function tests (ALT, AST, bilirubin, albumin) - assesses liver damage
Critical Pitfalls to Avoid
- Never rely on vaccination history alone to exclude HBV infection in persons from endemic areas or with risk factors, as they may have been infected before vaccination. 1
- Do not delay testing in exposed individuals - the first dose of hepatitis B vaccine should be administered immediately after blood collection for testing, not after results return. 1
- Isolated HBsAg positivity requires confirmation with additional markers, as false-positive results can occur due to heterophilic antibody interference. 3
- HBV DNA testing can detect infection 10-20 days before HBsAg becomes positive, but this is not routinely used for initial screening due to cost and complexity. 1