What is the only positive marker present during the window period of hepatitis B?

During the window period of hepatitis B, the only positive marker is HBV DNA. The window period refers to the phase in the hepatitis B infection when the surface antigen (HBsAg) may no longer be detectable (due to clearance of the virus), but the antibodies against the virus (specifically Anti-HBs) are not yet present because the immune response is still developing.

At this point, HBV DNA is detectable, indicating that the virus is still present in the body, even though other serological markers may not be available. Therefore, HBV DNA serves as a crucial indicator of active viral replication during this time.

In contrast, Anti-HBc would typically be present after the initial infection has occurred, but during the window period, HBsAg might be cleared, making it a less reliable marker at that stage. Anti-HBs is the antibody that develops in response to HBsAg and signals recovery or vaccination; it is not detectable until later in the infection. Thus, HBV DNA is the only marker that remains positive during the window period of hepatitis B.