Discordant serum CA 125 values in commercial immunoassays

The CA 125 assay is from a clinical point of view very well suited to monitor ovarian cancer patients. Although most commercial assay systems include as standards CA 125 preparations derived from the OVCA 433 cell line, the various assay configurations do not produce identical results. The so called cut-off value of 35 U/ml obtained in the original Centocor CA 125 assay appears to be equivalent to CA 125 values ranging as low as 18 U/ml and as high as 53 U/ml in other commercial CA 125 assays now available. Because of these dissimilar results, obtained with different immunoassays, switching from one assay to another during follow-up, should not be tolerated. The newly introduced second generation Centocor CA 125 II IRMA was shown to retain the cut-off values of 35 U/ml and 65 U/ml as defined with the original CA 125 IRMA.