CCNA was developed to detect the presence of C. difficile toxin in fecal samples.
In this assay, a filtrate of stool sample is prepared and inoculated onto sensitive tissue culture cells. Typically human fibroblast cells are utilized; if toxin is present in the filtrate, it causes the fibroblasts to round up in a characteristic cytopathic effect.
To verify that the cytopathic effect is in fact caused by C. difficile toxin (and not by some other toxic component or viral agent) the filtrate is also inoculated in parallel onto a second set of tissue culture cells, to which C. difficile specific anti-toxin has been added.
Absence of the cytopathic effect in the second set of cell cultures provides evidence that the cellular changes in the first set were caused by C. difficile toxin.
Although CCNA is considered one of the best testing methods for the detection of C. difficile toxin, it is labor intensive, requires the use of cell cultures, and requires at least 48 hours incubation.