EIA versus RIA in Detecting Carcinoembryonic Antigen Level of Patients with Metastatic Colorectal Cancer

Background/Aims: Little literature exists comparing the differences between enzyme immunoassay (EIA) and radioimmunoassay (RIA) in the detection of serum carcinoembryonic antigen (CEA) levels of patients with metastatic colorectal cancer. Because EIA has the advantage of avoiding the use of radioisotopes, the potential of using EIA instead of RIA in detecting CEA of patients with colorectal cancer is of interest to us. Methodology: Between March and August 2001, a total of 120 blood specimens, including 60 specimens from patients with metastatic colorectal cancer and another 60 from patients with non-malignant diseases, were examined in this study. Serum CEA levels were examined by EIA and RIA methods in parallel. The CEA-EIA tests were done using EIA kits manufactured by Abbott Laboratories at Illinois in the United States. Comparison was done with the conventional CEA-RIA tests using RIA kits manufactured by CIS laboratory at France. The blood samples were sent to Veterans General Hospital-Taipei for EIA and RIA determination. The cut-off value for CEA was set at 5.0ng/mL. Results: The correlation between the Abbott-EIA and the CIS-RIA methods in detecting serum CEA levels was high. The results give a correlation coefficient of 0.992 with a linear regression line y=0.975 x + 0.215 (p<0.0001). Agreement in the Abbott-EIA and CIS-RIA tests in diagnosis was observed in 113 patients (94%), including 53 positive (>5ng/mL) and negative (<5ng/mL) in both tests. The sensitivity was similar in both assays (83% vs. 80%) at a cut-off level of 5ng/mL. The ability to discriminate between colorectal cancer and non-malignant diseases was good in both assays (p<0.001). The specificity and positive predictive value were slightly higher with the Abbott-EIA method compared with CIS-RIA assay (92% vs. 83% and 91% vs. 83%, respectively). The Abbott-EIA method achieved a similar diagnostic accuracy to CIS-RIA method (88% vs. 82%). Conclusions: These data suggest that the Abbott-EIA has similar diagnostic power to CIS-RIA in the measurement of CEA levels of patients with metastatic colorectal cancer, with an additional advantage of avoiding the use of radioisotopes. We believe that EIA has the potential to replace RIA in the measurement of CEA in clinical practice.