Fresenius Nurse Practice Test 2026 - Free Practice Questions and Study Guide for Fresenius Nurses

HBsAg is the hepatitis B surface antigen; its presence in the blood means the person is currently infected with hepatitis B. It appears early after exposure and can be seen in both acute and chronic infection. If it remains detectable for more than about six months, the infection is considered chronic. In contrast, antibodies to the surface (HBsAb) indicate immunity from vaccination or recovery, antibodies to the core (Anti-HBc) show exposure to the virus (with IgM suggesting a recent infection and IgG indicating past or chronic exposure), and the surface antigen’s counterpart HBeAg reflects active viral replication and high infectivity but is not the direct marker of current infection itself. Therefore, the marker that best indicates active hepatitis B infection is the surface antigen.