Evaluation of a latex agglutination test for diagnosis of Clostridium difficile-associated colitis

Current methods for diagnosis of Clostridium difficile-associated colitis (CAC) based on detection of cytotoxin B by a tissue culture assay (TCA) require technical expertise and up to 48 hours incubation. Recently, a latex agglutination (LA) test (Marion Laboratories) for rapid diagnosis of CAC has become available. Although early evaluations have been favorable, new evidence suggests that the LA reagent binds a soluble bacterial antigen that is not unique to toxigenic strains of C. difficile. The authors examined 201 stools received for CAC testing by LA and a reference TCA and investigated discrepant results. They obtained 29 LA(+)/TCA(+) and 155 LA(-)/TCA(-) results. Eleven patients had LA(+)/TCA(-) results and 6 had LA(-)/TCA(+) results. The sensitivity and specificity of the LA were 83% and 93%, respectively, compared with TCA. The predictive values of positive and negative results obtained with the LA were 72% and 96%, respectively. Concentrated broth supernatants and liver suspensions of three C. difficile isolates with LA(+)/TCA(-) results were tested in a rabbit ileal loop assay. All failed to demonstrate ability to produce an enterotoxin. The authors conclude that the LA method is suitable for rapid screening, but LA(+) results require confirmation by testing with other methods.