Which laboratory finding is indicative of an acute Hepatitis B infection?

A positive HBsAg indicates that the Hepatitis B virus is actively replicating in the body. HBsAg, or Hepatitis B surface antigen, is the first serological marker that becomes detectable during an acute HBV infection and typically appears within 1-10 weeks after exposure. The presence of HBsAg is essential for the diagnosis of acute hepatitis B, as it confirms that the virus is currently present in the bloodstream and the individual is potentially infectious.

In contrast, the other markers listed provide different information that does not directly indicate an acute infection. For example, negative Anti-HBs suggests that there is no immunity to Hepatitis B, while a positive Anti-HBc would imply past or current infection but does not specifically confirm active infection as HBsAg does. Positive Anti-HBe indicates low levels of viral replication and may be seen in chronic infections but is not a primary indicator of an acute infection. Therefore, HBsAg is the definitive laboratory finding for confirming an acute Hepatitis B infection.