Evaluation of the usefulness of counterimmunoelectrophoresis for diagnosis of Clostridium difficile-associated colitis in clinical specimens.

Results of counterimmunoelectrophoresis (CIE) were compared with those of isolation of Clostridium difficile and assay for cytotoxicity in HeLa cells. On the basis of 471 stool specimens, CIE exhibited a sensitivity of 38% and a specificity of 88% as compared with the cytotoxin assay. The predictive value of a reactive CIE results is low (17%), whereas the predictive value of a nonreactive CIE result is significant (96%) and therefore warrants its use as a screening test. In addition, stool filtrates may nonspecifically precipitate with the C. difficile antitoxin in the CIE test. Such nonspecific reactions may be identified by simultaneous electrophoresis against nonimmune serum.