Cutoff levels of immunoglobulin M antibody against viral core antigen for differentiation of acute, chronic, and past hepatitis B virus infections.

The titer of antibody against core antigen of hepatitis B virus in the immunoglobulin M class (IgM anti-HBc) was determined by an IgM capture assay of reduced sensitivity (30 arbitrary units). The distribution of titers among 235 acute hepatitis patients who were hepatitis B surface antigen (HBsAg) positive suggested that 600 U forms a lower cutoff value for acute hepatitis B. Clinically apparent cases of acute hepatitis with high IgM anti-HBc and without HBsAg were rare (2.6%). Acute, non-B hepatitis in HBsAg carriers was more frequent (9.4%). In chronic hepatitis B, 39% of 174 biopsy-proven cases had moderate titers of 30 to 600 U, whereas healthy HBsAg carriers were rarely (4/84) positive. In mild or inapparent infections without HBsAg, titers were between 50 and 400 U. Thus, sufficiently accurate and sensitive quantitation of IgM anti-HBc allows for differentiation of acute and nonacute hepatitis B virus infection in acute hepatitis, partial differentiation between clinically symptomatic and asymptomatic chronic infections, and identification of recent subclinical infections.