For diagnosis of acute hepatitis, tests called assays involve blood tests that detect either viral antigens(proteins produced by the virus) or antibodies produced by the host. Interpretation of these assays is complex. The hepatitis B surface antigen(HBsAg) is most frequently used to screen for the presence of this infection. It is the first detectable viral antigen to appear during infection. However, early in an infection, this antigen may not be present and it may be undetectable later in the infection as it is being cleared by the host.
Attribution: Avallain