Proficiency testing for the radioimmunoassay of carcinoembryonic antigen. A one-year report

Forty-three laboratories participated in an interlaboratory testing program offered by the College of American Pathologists for the radioimmunoassay (RIA) of carcinoembryonic antigen (CEA). Thirty correctly reported a sample with 1.9 ng of endogenous CEA per ml as less than 2.5 ng. For samples with added exogenous CEA at the 5.4 ng/ml level, 24 laboratories reported too low and six too high (more than 2 SD beyond the targe value). At the 8.9 ng/ml concentration, three laboratories underestimated the CEA, while 18 overestimated the sample's concentration. A similar proportion of the laboratories performed in the same manner when estimating CEA at a target concentration of 15.9 ng/ml (five underestimating and 27 overestimating the concentration). Although individual variations were large, the majority of participating laboratories can reliably distinguish normal concentrations of CEA from moderate, intermediate and large elevations.