Comparison of one first 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, one step immunoradiometric assays (IRMA) to detect the CA 125 glycoprotein. Recently, two step IRMA's were developed, the CA 125 II 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 the tracer. We compared analytically and clinically one first generation radioassay, and three second generation assays (two radioassays and one ELISA). 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 and the second generation methods really satisfied, however the cut off 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 concentration during disease monitoring is not reliable when different determination methods are used consecutively.