Evaluation of second generation CA 125 assays

Objective: This study was performed in order to evaluate and compare the serum CA 125 values obtained using an immunoradiometric (IRMA-II) and an immunoenzymatic (ETI-II) second generation assay, and to establish whether or not the two methods may be used interchangeably. Study design: Serum CA 125 levels were measured in parallel using IRMA-II and ETI-II CA 125 assays (Sorin Biomedica), in 82 women with benign or malignant gynecological diseases. Statistical analysis was performed by linear regression analysis and Wilcoxon's test. Results: Serum CA 125 levels measured using the immunoenzymatic method were lower than those obtained by the immunoradiometric assay. The largest discrepancies between the two methods were found at concentrations of 35-100 U/ml, within which fall cutoff values for the immunoradiometric assay. The cutoff values of 35 or 65 U/ml, frequently used in the original immunoradiometric assay and retained for the immunoradiometric second generation assay, corresponded to 18 and 47 U/ml in the immunoenzymatic second generation assay. Conclusion: The discrepancies in CA 125 results obtained by the two detection methods imply that the cutoff values used in the immunoenzymatic procedure should have a lower reference value in order to eliminate high rates of false negative results. Furthermore, their interchangeable use should be avoided in the monitoring of ovarian cancer and other gynecological diseases.