Serodiagnosis of acute B hepatitis: comparison between a competitive binding radioimmunoassay and an enzyme linked immunosorbent assay for IgM antibody to hepatitis B core antigen.

The standard radioimmunoassay for anti-HBc (CORAB) was modified for the differential detection of anti-HBc IgM by incorporation of a step in which anti-HBc IgG was preferentially absorbed by Staphylococcus aureus cells (Protein A). The ratio (R) of anti-HBc IgM to total anti-HBc was evaluated by computing the ratio of sample cpm's after and before protein A absorption. The R values of acute B hepatitis ranged from 0.9 to 2.1 (mean 1.3 +/- 0.3) while those of chronic HBsAg carriers ranged from 3.1 to 8.3 (mean 4.9 +/- 1.1). Adopting 2.1 as the upper limit of R value for acute B infection, this modified CORAB was shown to have excellent correlation with enzyme immunoassay, and to be capable of differentiating acute from persistent HBV infection in HBsAg positive patients, and discriminating acute B hepatitis from non-A, non-B hepatitis in HBsAg negative but anti-HBc positive acute hepatitis.