Radioimmunoassay inhibition method for confirming the specificity of positive hepatitis B surface antigen reactions and for survey of antibodies to the antigen.

Studies were conducted to determine the hepatitis B surface antigen antibody (anti-HBS) levels and antibody subtype specificities required in order for anti-HBS sera of human origin to be suitable for use in radioimmunoassay (RIA) inhibition tests for determining the specificity of positive reactions for hepatitis B surface antigen (HBSAg). Also, the RIA inhibition method was evaluated for detection of anti-HBS in sera of laboratory personnel. Only anti-HBS sera with complement-fixing (CF) antibody titers of 1:32 or higher effectively inhibited HBSAg-positive sera with demonstrable CF activity, and complete inhibition was obtained only for antigens having CF titers of 1:64 or lower. Higher-titered antigens could be inhibited when diluted 1:10-1:100. The low-titered HBSAg preparation supplied with AusRIA kits (Abbott Laboratories) was effectively inhibited by low-titered anti-HBS sera, and when used in RIA inhibition tests on sera from laboratory personnel, the tests detected anti-HBS in approximately 14% of the individuals tested, a slightly greater number than those showing anti-HBS in passive hemagglutination tests. Inhibition of HBSAg-positive sera by the anti-HBS sera could not be related to the d and y subtype specificities of the antigens or antisera; the antisera were no more effective in inhibiting antigens of the homologous subtype than those of the heterologous subtype.