Two monoclonal-based assays for carcinoembryonic antigen compared

Monoclonal antibody-based methods can provide clinically different impressions for some patients than does an earlier method involving a conventional antiserum. Therefore, performance of two commercial double-monoclonal-antibody methods for carcinoembryonic antigen (CEA) were studied further, those of Abbott Diagnostics and Roche Diagnostic Systems. The two methods showed similar precision. Total CVs over 20 days at three concentrations were 16, 6, and 6% in the Roche assay, and 15, 8, and 7% in the Abbott assay (n = 20). Within-run CVs for quality-control levels 1, 2, and 3, respectively, in the Roche assay were 14, 8, and 9%, and in the Abbott 15, 9, and 10% (n = 20). Mean CEA concentrations were consistently lower in the Roche assay than in the Abbott assay. Results of the two assays correlated significantly in patients with CEA-secreting carcinomas (r = 0.88), and in serial samples from cancer patients who had low, medium, or high CEA concentrations in their sera (r = 0.92 for all serial data). About 10% of values were false-positive (greater than 5.0 micrograms/L) by each of the two methods in 89 patients with various non-malignant conditions. The two methods appear to be more specific for tumor-associated CEA than are polyclonal antibody-based assays previously available from the two manufacturers.