Effective detection of toxigenic Clostridium difficile by a two-step algorithm including tests for antigen and cytotoxin

We evaluated a two-step algorithm for detecting toxigenic Clostridium difficile: an enzyme immunoassay for glutamate dehydrogenase antigen (Ag-EIA) and then, for antigen-positive specimens, a concurrent cell culture cytotoxicity neutralization assay (CCNA). Antigen-negative results were >= 99% predictive of CCNA negativity. Because the Ag-EIA reduced cell culture workload by approximate to 75 to 80% and two-step testing was complete in <= 3 days, we decided that this algorithm would be effective. Over 6 months, our laboratories' expenses were US$143,000 less than if CCNA alone had been performed on all 5,887 specimens.