Analytical and clinical performance of improved Abbott IMx CA 125 assay: comparison with Abbott CA 125 RIA

We compared the improved Abbott IMx cancer antigen (CA) 125 assay (cat. no. 7A89) with the Abbott CA 125 RIA. Serum specimens were from healthy perimenopausal women (n = 124) and from patients with benign gynecologic and nongynecologic diseases (n = 124), ovarian carcinoma (n = 104), or other malignancies (n = 193). The IMx assay detected as little as 0.193 kAU/L CA 125 (AU = arbitrary Abbott unit), demonstrated up to 29% overestimation upon serum dilution, low within-assay (2.7-5.6%) and between-assay (4.8-8.2%) CVs, and no high-dose hook effect < or = 46,000 kAU/L nor influence from human anti-mouse antibodies in serum of women injected with OC 125 F(ab')2. Values by IMx were 20% lower than by RIA for healthy perimenopausal women (n = 100; IMx = 0.80 RIA - 2.5 kAU/L), and at least 50% higher for those with benign or malignant ovarian disorders at concentrations < 100 kAU/L. Receiver-operating characteristic (ROC) curve analysis of ovarian neoplasma vs perimenopausal controls indicated a gain of specificity and sensitivity with the improved IMx assay over the RIA, but ROC performance was the same with either assay if patients with benign ovarian disorders were used as controls.