Specificity of an assay for antibodies to hepatitis B surface antigen.

Eight percent of blood donors were found to have antibodies to hepatitis B surface antigen when tested by radioimmunoassay using commercial test kits. Four percent of positive reactions proved nonspecific when tested by the neutralization test using pooled surface antigen. The risks in relying solely on the reactivity in commercial-kit suggested that the specificity of the assay must be confirmed.