Comparison of enzyme immunoassay with radioimmunoassay for the detection of antibody to hepatitis B core antigen as the only marker of hepatitis b infection in a population with a high prevalence of hepatitis B

Enzyme immunoassay (EIA) and radioimmunoassay (RIA) for the detection of antibody to hepatitis B core antigen (anti‐HBc) were compared using serum specimens from Alaska Natives screened during a hepatitis B control program that were initially positive by EIA for only anti‐HBc. Of 36 specimens from persons previously HBsAg positive but who were now only anti‐HBc positive by EIA, 94.4% were anti‐HBc positive by both assays, with anti‐HBc levels exceeding 93% inhibition. Low‐level antibody to hepatitis B surface antigen (anti‐HBs) (<10 SRU) and antibody to hepatitis Be (anti‐HBe) were also present in 50% and 48% of specimens positive for anti‐HBc, respectively. Of 148 specimens from persons initially positive for only anti‐HBc by EIA who had no previous documentation of any hepatitis B virus (HBV) infection, 64.5% were positive by repeat testing for anti‐HBc by both assays, and anti‐HBc levels in this sample exceeded 70% in 91.6% and 80.2% of specimens by EIA and RIA, respectively. Low‐level anti‐HBs and anti‐HBe were present in 45.8% and 15.6%, respectively. EIA detection of anti‐HBc was found to be less specific than RIA. Of specimens positive for anti‐HBc by EIA, 14.8% were negative by RIA. The specificity of the EIA could be improved with respect to RIA by increasing the cut‐off from 48% to 68%. In samples with lowlevel anti‐HBc (≧70% inhibition) as measured by either method, the anti‐HBc results was less likely to persist upon retesting, whereas sample with anti‐HBc levels of >70% inhibition the anti‐HBc was a reproducible finding frequently accompanied by either low‐level anti‐HBs or anti‐HBe.