From the Guidelines
The hepatitis B surface antigen (HBsAg) test is the screening test that indicates a current hepatitis B infection when positive. This test detects the viral protein present on the surface of the hepatitis B virus, which appears in the blood during active infection. A positive HBsAg result typically becomes detectable 1-10 weeks after exposure and indicates that the person is infectious [ 1 ]. If HBsAg persists for more than 6 months, this suggests chronic hepatitis B infection. The test is important because it helps identify both symptomatic and asymptomatic infections, allowing for appropriate management and prevention of transmission. Other markers like hepatitis B e antigen (HBeAg) may provide additional information about viral replication and infectivity, while antibody tests such as anti-HBc (core antibody) and anti-HBs (surface antibody) help distinguish between current infection, past infection, or immunity from vaccination [ 1 ]. However, HBsAg remains the primary marker that directly indicates current hepatitis B infection.
Some key points to consider when interpreting HBsAg test results include:
- A positive HBsAg result indicates active HBV infection [ 1 ]
- HBsAg testing is the primary tool for screening and diagnosis of HBV infection [ 1 ]
- Confirmation of positive HBsAg findings should be confirmed by a second test at a different time point [ 1 ]
- The presence of a confirmed HBsAg-positive result in serum indicates active HBV infection, and all HBsAg-positive persons should be considered infectious [ 1 ]
It's worth noting that the HBsAg test has a high sensitivity and specificity, with values greater than 98% [ 1 ]. This makes it a reliable test for detecting current hepatitis B infection. Overall, the HBsAg test is a crucial tool for identifying and managing hepatitis B infection, and its results should be interpreted in the context of clinical presentation and other laboratory tests.
From the Research
Hepatitis B Screening Tests
- The hepatitis B surface antigen (HBsAg) test is a key marker for screening and laboratory diagnosis of HBV infection 2.
- A positive HBsAg test result indicates a current infection with hepatitis B virus.
- The HBsAg test is highly sensitive and specific, with a sensitivity of 98.3%-99.3% and a specificity of 98.0%-99.5% 2.
Interpretation of Test Results
- A positive HBsAg test result, in combination with other markers such as hepatitis B core antigen, can indicate acute or chronic hepatitis B infection 3.
- The presence of HBsAg in the blood for more than six months is indicative of chronic hepatitis B infection 3.
- It is essential to note that HBsAg testing alone may not be sufficient to detect all chronic HBV infections, as some individuals may have occult HBV infection (OBI) despite being HBsAg-negative 4.
Diagnostic Tests
- Rapid diagnostic tests (RDTs) for HBsAg detection in serum or plasma are available and have been shown to be highly sensitive and specific 2.
- These RDTs can be used for large-scale screening and diagnosis of HBV infection in clinical settings.
- Examples of RDTs with high sensitivity (≥99%) include the VIKIA HBsAg and First Response HBsAg Card Test 2.