Which of the following is incorrect about the diagnosis of Clostrium difficile-related pseudomembranous colitis?
A. The most popular diagnostic test is a tissue culture assay for a cytotoxin that is elaborated by C. difficile.
B. Because nontoxigenic strains of C. difficile can be isolated in the stool of asymptomatic patients, tests that document the presence of C. difficile in stool (i.e., stool culture or latex agglutination test) lack specificity.
C. The cytotoxin assay has high sensitivity, performing serial stool cytotoxin assays is not necessary
D. Direct visualization with proctosigmoidoscopy or colonoscopy of the lower GI mucosa is a valuable but underused diagnostic test for C. difficile colitis.
Answer: C
As many as 30% of patients with presumed C. difficile colitis (positive cultures and pseudomembranes) can have a negative cytotoxin assay on a single stool specimen (13,14), so the cytotoxin assay lacks sensitivity. Performing serial stool cytotoxin assays is recommended to improve the sensitivity of the C. difficile cytotoxin assay.
Reference
Paul L. Marino. THE ICU BOOK. Second Edition