HETEROLOGOUS DOUBLE-DETERMINANT IMMUNORADIOMETRIC ASSAY CA-125-II - RELIABLE 2ND-GENERATION IMMUNOASSAY FOR DETERMINING CA-125 IN SERUM

The new CA 125 II (Centocor) serum assay utilizing the M11 mouse monoc lonal antibody as capture antibody and OC125 as tracer antibody, was i nvestigated for its technical and clinical performance against the ori ginal CA 125 assay. The CA 125 II test revealed a quadruple increase i n signal-to-noise ratio, good intra- and interassay precision (with CV s<5% and 7%, respectively), improved dilution linearity, and a minimal detectable dose of 0.38 units/mL. Sera were obtained from healthy fem ales (n= 192), women with benign conditions (n=208), and patients with various cancers (n=379). Both assays measured highly similar CA 125 d istributions with equal reference ranges and nearly identical positivi ty (>35 units/mL) rates, resulting in similar receiver-operating chara cteristic curves and monitoring graphs. Linear regression analysis of results by the two assays (CA 125=x, CA 125 II=y) in ovarian cancer pa tients showed, for CA 125 assay values between 0 and 1000 units/mL, a slope of 1.00 and a y-intercept of 12.6 (n=254, r=0.8617, P<0.0001). T he heterologous CA 125 II assay appeared to be more accurate in patien ts who had human anti-mouse antibodies after immunoscintigraphy. The C A 125 II immunoradiometric assay is sensitive and reliable for measuri ng serum CA 125, and fully retains the cutoff values of 35 and 65 unit s/mL that were defined with the original CA 125 immunoradiometric assa y.