Measurement of CA 125 by an automated microparticle enzyme immunoassay; comparison with a manual enzyme immunoassay

Abstract

The technical characteristics and the clinical usefulness of a new automated microparticle enzyme immunoassay (Abbott IMx^R CA 125) for cancer antigen 125 (CA 125) in serum were investigated. The microparticle enzyme immunoassay (MEIA) had a high degree of practicability and a short turn-around-time. The imprecision (2.5–6.4%), detectability (< 1 kU 1⁻¹), and carryover (less than 0.01%) of the analysis were low and the recovery of CA 125 after dilution with serum from ovarian cancer patients was good. The antigen was measured in samples from 72 ovarian cancer patients by the MEIA and a well documented manual enzyme immunoassay (Abbott CA 125 El A). The correlation between the CA 125 MEIA and EIA results was non-linear. CA 125 EIA values below 39 kU 1⁻¹ (95% CI: 36–42) gave higher MEIA results and EIA values above this level resulted in lower MEIA values. The marker was measured before second-look laparotomy of 57 ovarian cancer patients. Using different cut-off levels, the clinical information of CA 125 MEIA measurements was equivalent to that obtained by EIA. The relationship between the CA 125 EIA values and the corresponding MEIA results was complex and the clinician may have difficulties in interpreting the MEIA CA 125 results until the calibration has been approximated to that of EIA. Alternatively, clinical investigations should be performed to establish an upper reference limit of MEIA CA 125 values.

Key Words:

• assay characteristics
• cancer antigen 125
• ovarian cancer