Comparison of one first-generation and three second-generation methods for the determination of CA 125

The monoclonal antibody OC125 (Centocor, Inc, Malvern, PA) was the basis for the first generation of one-step immunoradiometric assays (IRMA), used to detect the glycoprotein CA 125. Recently two-step IRMAs were developed: the CA 125 second-generation assays. In these new assays the CA 125 capture antibody is the M11 monoclonal antibody coated on a solid phase and the OC125 monoclonal antibody is used as tracer. We compared one first-generation radioassay and three second-generation assays (two radioassays and one ELISA) both analytically and clinically. The ELISA method showed the best within-assay precision and the best curve fitting characteristics. In the clinical comparison, none of the correlations between the first-generation and second-generation methods were really satisfactory; however, the cutoff level of 35 U/ml was confirmed. The four CA 125 assays do not yield equal results. As a consequence, the evolution of CA 125 serum concentrations during disease monitoring is not reliable when different determination methods are used consecutively.