Micrograph of a colonic pseudomembrane in C.<unk>  colitis, a type of pseudomembranous colitis, H&E stain Endoscopic image of pseudomembranous colitis, with yellow pseudomembranes seen on the wall of the sigmoid colon Pseudomembranous colitis on computed tomography Prior to the advent of tests to detect C.<unk>  toxins, the diagnosis most often was made by colonoscopy or sigmoidoscopy. The appearance of "pseudomembranes" on the mucosa of the colon or rectum is highly suggestive, but not diagnostic of the condition. The pseudomembranes are composed of an exudate made of inflammatory debris, white blood cells. Although colonoscopy and sigmoidoscopy are still employed, now stool testing for the presence of C.<unk>  toxins is frequently the first-line diagnostic approach. Usually, only two toxins are tested for—toxin A and toxin B—but the organism produces several others. This test is not 100% accurate, with a considerable false-negative rate even with repeat testing. Cytotoxicity assay C.<unk>  toxins have a cytopathic effect in cell culture, and neutralization of any effect observed with specific antisera is the practical gold standard for studies investigating new CDI diagnostic techniques. Toxigenic culture, in which organisms are cultured on selective media and tested for toxin production, remains the gold standard and is the most sensitive and specific test, although it is slow and labor-intensive. Toxin ELISA Assessment of the A and B toxins by enzyme-linked immunosorbent assay (ELISA) for toxin A or B (or both) has a sensitivity of 63–99% and a specificity of 93–100%. Previously, experts recommended sending as many as three stool samples to rule out disease if initial tests are negative, but evidence suggests repeated testing during the same episode of diarrhea is of limited value and should be discouraged. C.<unk>  toxin should clear from the stool of somebody previously infected if treatment is effective. Many hospitals only test for the prevalent toxin A. Strains that express only the B toxin are now present in many hospitals, however, so testing for both toxins should occur. Not testing for both may contribute to a delay in obtaining laboratory results, which is often the cause of prolonged illness and poor outcomes. Other stool tests Stool leukocyte measurements and stool lactoferrin levels also have been proposed as diagnostic tests, but may have limited diagnostic accuracy. PCR Testing of stool samples by real-time polymerase chain reaction is able to detect C.<unk>  about 93% of the time and when positive is incorrectly positive about 3% of the time. This is more accurate than cytotoxigenic culture or cell cytotoxicity assay. Another benefit is that the result can be achieved within three hours. Drawbacks include a higher cost and the fact that the test only looks for the gene for the toxin and not the toxin itself. The latter means that if the test is used without confirmation, overdiagnosis may occur. Repeat testing may be misleading, and testing specimens more than once every seven days in people without new symptoms is highly unlikely to yield useful information.
Clostridioides difficile infection
Antibiotic-associated diarrhea
Irritable bowel syndrome
Campylobacteriosis
Gay bowel syndrome
Wilderness-acquired diarrhea
Factitious diarrhea
Cytomegalovirus colitis