Specificity of enzyme immunoassay for hepatitis B core antibody used in screening blood donors.

Hepatitis B core antibody (anti-HBc) is currently tested by a competitive inhibition enzyme immunoassay (EIA), using recombinant DNA-produced core antigen. We have used the anti-HBc assay in routine screening of voluntary blood donors in San Francisco. The detection rate of anti-HBc was 2.08 percent. The specificity of the antibody test was established by an absorption method using purified HBc antigen (HBcAg) produced by recombinant DNA technology and covalently coupled to Sepharose 4B. Bovine serum albumin was used in the preparation of a control conjugate. The absorption test demonstrated that out of 98 anti-HBc-positive specimens, 97 could be specifically neutralized. Only one specimen was indeterminate. The absorption test was particularly useful in confirming the specificity of EIA in eight specimens inconsistently positive for anti-HBc. We conclude that the current EIA for anti-HBc is highly specific and we are of the opinion that it could be used as a rational basis for donor deferral since it gives evidence of active or previous HBV infection.