During the 'window period', what is the only marker of HBV infection?

During the 'window period', what is the only marker of HBV infection?

• A. HBsAg
• B. HBV DNA
• C. Anti-HBs
• D. Anti-HBc

Answer: (D)

During the window period, the virus is no longer releasing detectable surface antigen, and the protective anti-HBs antibody has not yet appeared. The immune system is still mounting a response to the core antigen, so anti-HBc becomes the only serologic marker that indicates HBV infection at this stage. This core antibody response, especially IgM anti-HBc, signals recent infection even when HBsAg is negative and anti-HBs is not yet detectable. HBV DNA might be present, but the standard serologic marker used to identify infection in the window period is anti-HBc.

During the window period, the virus is no longer releasing detectable surface antigen, and the protective anti-HBs antibody has not yet appeared. The immune system is still mounting a response to the core antigen, so anti-HBc becomes the only serologic marker that indicates HBV infection at this stage. This core antibody response, especially IgM anti-HBc, signals recent infection even when HBsAg is negative and anti-HBs is not yet detectable. HBV DNA might be present, but the standard serologic marker used to identify infection in the window period is anti-HBc.