COMPARISON OF 4 2ND-GENERATION IMMUNOASSAY SYSTEMS TO DETERMINE CA-125 IN SERUM BY USING A GRAPHICAL APPROACH TO METHOD COMPARISON ANALYSIS

Clinical management of ovarian cancer patients is facilitated by CA 12 5 determinations in serum. Presently, several assay systems based on d ifferent concepts and different methodologies are available to measure CA 125. Method comparison analysis of such assay systems is usually p erformed through (linear) regression analysis, which requires assumpti ons about the distribution of experimental data and its measurement er ror. The aim of the present study was to compare four newly developed second generation assay systems for quantitation of CA 125 by utilizin g an alternative simple approach to method comparison analysis. This a lternative comprises the construction of relative difference plots and mountain plots, previously described by Krouwer et al. (fur J Clin Ch em Clin Biochem 1995; 33:525-7). In addition, the diagnostic value of the assays was illustrated through receiver-operating-characteristic ( ROC) curves. Sera obtained from 300 women were assayed for CA 125 usin g the Abbott IMx CA 125 assay (Abbott), the Centocor CA 125 II RIA ass ay (Centocor), the Berilux Ov testing kit for CA 125 (Behringwerke), a nd the CA 125 TR-FIA assay (Wallac Oy). Both the relative difference p lots and the mountain plots revealed higher serum concentrations with the Centocor RIA II (Median +33%, P-2.5 to P-97.5: -25% to 161%) and B erilux (Median +28%, P-2.5 to P-97.5: -17% to 108%) compared to the Ab bott IMx system. The TR-FIA assay system showed lower serum concentrat ions (Median -17%, P-2.5 to P-97.5: -74% to 229%). The combination of relative difference plots and mountain plots demonstrated clearly the wide range of differences between CA 125 assays measuring the same ana lyte. The relative difference plots provided insight into the distribu tion of the differences over the range of measurement as well as the i dentification of outliers. A simple quantitative assessment of the med ian differences could be made from the overlaying mountain plots. The close correspondence observed between the ROC curves illustrated that assay systems for CA 125 differing in design (type of antibodies used) and format can produce similar results on group level. However, the r esults of the clinical evaluation underline the importance of the appl ication of assay specific cut-off values.