Specificity of immunoassays. II. Heterogeneity of specificity of antibodies in antisera used for steroid immunoassay and the selective blocking of less specific antibodies, including a new method for the measurement of immunoassay specificity.

Practical aspects of the measurement of the specificity of immunoassay are reviewed. Antibody heterogeneity in an antiserum makes a pragmatic rather than a theoretical approach necessary. A new method for the measurement of immunoassay specificity is described. This method is based on the errors caused by the cross-reacting antigens and is directly relevant to the validity of results obtained by immunoassay methods. The effect of selectively blocking the least specific antibodies in antisera raised against steroid haptens is tested. The practical consequences of these considerations are tested using steroid radioimmunoassay and enzyme-immunoassay.