Analytical and clinical evaluation of a procedure for measuring CA 15-3 in the IMx analyser

CA 15-3 is the most widely used tumour marker in the follow-up of patients with breast cancer. Its postoperative blood level is closely related to the response to the treatment applied and to the evolution of the disease. In this study, we assessed both the clinical and analytical features of a new microparticle enzyme immunoassay for CA 15-3 quantification in the Abbott IMx system. In the precision study, the coefficients of variation within runs, between runs and between laboratories were 3.5, 5.1 and 6.5% or less, respectively. The analytical sensitivity of the assay was 0.11 U/ml. Linear regression analyses of the IMx CA 15-3 assay with the Centocor and CIS CA 15-3 RIAs gave correlation coefficients of 0.88 and 0.95, respectively. The upper limit of the reference range, obtained from serum of healthy women, was 27.3 U/ml, while the ROC curve analysis for patients with active breast cancer compared to patients with no evidence of the disease gave an optimum cutoff of 33 U/ml (sensitivity 0.76 and specificity 0.87). The overall agreement of the three methods was over 90%.