Introduction
Hepatitis B Virus (HBV) infection is a global health concern. HBV is a member of the Hepadnaviridae family and contains a partially double-stranded circular DNA genome. The Hepatitis B surface antigen (HBsAg) is a glycoprotein found on the viral surface. The virus has eight genotypes and nine serological subtypes. A common antigen, “a,” is subdivided into four antigenic determinants based on amino acid sequences at positions 122 and 166.
The presence of antibodies against HBsAg (anti-HBs) indicates immunity to HBV, either through natural infection recovery or vaccination. Chronic HBV carriers typically have persistent HBsAg without detectable anti-HBs antibodies. Anti-HBs antibodies emerge following viral clearance or successful immunization and may persist for years. If anti-HBs levels remain undetectable post-infection, the patient may progress to chronic HBV, occurring in approximately 5% of cases (Kao et al., 2002).
Clinical Significance
The detection of anti-HBs is crucial in evaluating immune status against HBV. A titer of ≥10 mIU/ml indicates protective immunity, either from vaccination or past infection. This is particularly important for healthcare workers, immunocompromised individuals, and those undergoing organ transplantation. In contrast, individuals with undetectable or low anti-HBs levels (<10 mIU/ml) may require further vaccination or monitoring for HBV exposure (Chen et al., 2006).
Test Principle
The test is based on an antigen-sandwich enzyme immunoassay (ELISA). Serum samples containing anti-HBs antibodies bind to recombinant HBsAg-coated microtiter wells. Following incubation and washing, an HBsAg-HRP conjugate is added to bind the attached anti-HBs antibodies. After another incubation and wash cycle, a chromogen-substrate solution is added, producing a blue color. The reaction is stopped with an acid solution, turning the color yellow, and absorbance is measured at 450 nm. The intensity of the color is proportional to the anti-HBs concentration in the sample.
References
• Chen, D., et al. (2006). Performance of a new-generation chemiluminescent assay for hepatitis B surface antigen. Clinical Chemistry, 52(8), 1592-1598.
• Kao, J.-H., et al. (2002). Genotypes and clinical phenotypes of hepatitis B virus in patients with chronic infection. Journal of Clinical Microbiology, 40(4), 1207-1209.
• Kimura, T., et al. (2002). Sensitive enzyme immunoassay for hepatitis B virus core-related antigens and their correlation to virus load. Journal of Clinical Microbiology, 40(2), 445.
• Kidd-Ljunggren, K., et al. (2002). Genetic variability in hepatitis B viruses. Journal of General Virology, 83, 1267-1280.
• Thibault, V., et al. (2006). Coexistence of hepatitis B surface antigen (HBsAg) and anti-HBs antibodies in chronic carriers: Influence of “a” determinant variants. Journal of Virology, 80(6), 2968-2975.