Clostridium difficile, as the causative agent in antibiotic-associated diarrhea, can best be detected using which of the following gold standard laboratory tests?

All of the mentioned tests may be used as detection assays for C. difficile. However, only the tissue culture toxin detection assay is the gold standard laboratory test. Laboratory diagnosis of C. difficile: Stool culture on selective media, such as CCFA (cefoxitin cycloserine fructose agar) or CCYA (cefoxitin cycloserine egg yolk agar). Stool culture is highly sensitive but not specific. Toxin demonstration is more meaningful and is done by : Enzyme immunoassay for toxin A and/toxins B in stool is rapid, but not sensitive. PCR for C. difficile toxin B gene in stool is highly specific and sensitive. Colonoscopy is highly specific if pseudomembranes are seen, but sensitivity is low. Histopathology of colonic pseudomembrane is also highly specific.