IMx^R CA 125^TM, an automated microparticle enzyme immunoassay: technical characteristics and clinical usefulness after recalibration

Abstract

A recently described automated microparticle enzyme immunoassay (Abbott IMx^R CA 125^TM) for cancer antigen 125 (CA 125) was recalibrated by the manufacturer to provide better agreement between the results of the IMx^R assay and other test methods for CA 125. The recalibrated microparticle enzyme immunoassay (MEIA_II) had low imprecision (2.9–11.9%), a low detection limit (less than 0.48 kU 1⁻¹), a low carryover (less than 0.014%), and CA 125 was linearly recovered after dilution. CA 125 was measured during treatment of 138 patients with ovarian cancer and the MEIA_II results were closely, but non-linearly, related to antigen values determined by a routinely used manual enzyme immunoassay (EIA) (Abbott CA 125 EIA). EIA levels below 167 kU I⁻¹ resulted in higher values when measured by the MEIA_II and CA 125 concentrations above 167 kU 1⁻¹ in the EIA gave lower MEIA_II values. CA 125 MEIA_II and EIA measurements before a second-look laparotomy of 57 patients with ovarian cancer demonstrated that, using slightly different upper limits of normal values (MEIA_II, 27 kU 1⁻¹; EIA, 20 kU 1⁻¹), the clinical information obtained from the MEIA_II was equivalent to that obtained from the EIA. In conclusion, switching from the EIA to the MEIA_II would indicate that series of samples should be analysed by both methods during a transfer period. The length of the period should depend on the obtained results.

Key Words:

• assay characteristics
• cancer antigen 125
• ovarian cancer