[Changes in the response time of anti-HBc IgM in a hepatitis B case load. Diagnostic implications].

Anti-HBc IgM were determined in 46 patients whose serum was positive for hepatitis B surface antigen (HBsAg). All sera were tested from 1:4000 up to 1:8128000 dilution with a radioimmunometric assay. Anti-HBc IgM persisted at detectable level for up 15 months from acute infection in more than 50% of the patients. High levels of anti-HBc IgM are seen only in the acute phase but it is difficult to establish a cut-off dilution displaying diagnostic value between current and remote infection. Anti-HBc IgM are always detectable in acute hepatitis B virus (HBV) so that the absence of HBc IgM in acute hepatitis with positive HBsAg allows to discard HBV as the causative agent and to suspect a non-B hepatitis (A, delta, NANB). On the contrary the presence of anti-HBc IgM in detectable amounts in patients with acute hepatitis and negative HBsAg makes possible the diagnosis of acute B virus hepatitis.