What laboratory value is indicative of an acute Hepatitis B infection?

The presence of Hepatitis B surface antigen (HBsAg) is a key laboratory marker indicative of an acute Hepatitis B infection. HBsAg appears in the blood during the acute phase of infection and serves as an initial marker for active virus replication. Detecting HBsAg indicates that the individual is currently infected with the Hepatitis B virus, and this status may lead to the development of symptoms associated with acute hepatitis.

The presence of HBsAg is often followed by the appearance of other markers, such as antibodies to the core antigen, but HBsAg is the first and most direct indicator of an acute infection. In clinical practice, healthcare practitioners look for HBsAg to confirm active infection, allowing for timely treatment and management options.

While other options such as anti-HBc and anti-HBs provide important information regarding past infections and immunity, they do not directly indicate ongoing acute infection. Specifically, anti-HBc appears after initial HBsAg detection and can indicate either acute or chronic infection, while anti-HBs signifies recovery and immunity, further differentiating the phases of Hepatitis B infection. Molecular detection of Hepatitis B virus RNA may also provide information regarding the viral load but is not routinely used as a first-line diagnostic marker for acute infection