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If you suspect you have a clostridioides difficile infection (CDI), receiving a quick diagnosis and treatment can make all the difference in your outcome. Since CDIs range from virtually symptomless to fulminant pseudomembranous colitis, receiving a quality exam is crucial to diagnosis. What follows is the typical manner in which CDIs are diagnosed, along with warning signs of more severe cases. Ultimately, CDI is considered a clinical diagnosis, meaning it is based not just on a diagnostic test but also other symptoms and a patient’s history. Because you can still have C. diff bacteria in your gut without having an active infection, the results of a diagnostic test are insufficient. Similarly, doctors do not test for “cure.”

Details Count

Patient History

A CDI diagnosis requires your doctor taking a careful history with a particular emphasis on antibiotic use during the previous three months. As some antibiotics are more often implicated in C.diff disease, knowing the type and duration of your antibiotic use can be helpful.

The doctor may ask you for a detailed description of your diarrhea, including its color, consistency, and frequency. This is an important detail in differentiating C.diff-related diarrhea from other causes. Other important factors include a history of fever, immunosuppression (from chemotherapy, HIV or other causes), a recent surgical procedure, recent stay in a healthcare facility, previous infection with C.diff, recent change in bowel habits, recent proton-pump inhibitor use, and the presence of abdominal symptoms.

Identifying Specifics

Laboratory testing

Toxins produced by C.difficile bacteria can usually be detected in a sample of your stool. Several main types of lab tests exist, and they include:

  • Polymerase chain reaction. This sensitive molecular test can rapidly detect the C.difficile toxin B gene in a stool sample and is highly accurate.
  • GDH/EIA. Some hospitals use a glutamate dehydrogenase (GDH) test in conjunction with an enzyme immunoassay (EIA) test. GDH is a very sensitive assay and can accurately rule out the presence of C.difficile in stool samples.
  • Enzyme immunoassay. The enzyme immunoassay (EIA) test is faster than other tests but isn’t sensitive enough to detect many infections and has a higher rate of falsely normal results. This is typically not the only test used.
  • Cell cytotoxicity assay. A cytotoxicity test looks for the effects of the C.difficile toxin on human cells grown in a culture. This type of test is sensitive, but it is less widely available, is more cumbersome to do and requires 24 to 48 hours for test results. It’s typically used in research settings.
  • Blood tests are also important in the diagnosis of C.diff colitis, particularly as an indication of impending fulminant colitis. A sudden rise in the peripheral white blood cell count is an invaluable signal that progression to shock or toxic megacolon is imminent.
Getting a better look

Flexible Sigmoidoscopy and Colonoscopy

A flexible sigmoidoscopy is an examination where a fiberoptic tube with a light and camera on its end is inserted into the rectum and the sigmoid colon. In most people with C. diff colitis, pseudomembranes will be visible in the rectum and sigmoid colon.

Ruling out other issues


X-ray examinations and computed-tomography (CT) examinations of the abdomen will occasionally demonstrate thickening of the wall of the colon due to inflammation, but these x-ray findings are non-specific, revealing only that colitis is present but not its cause (e.g. C. diff). They may be used to rule out other conditions, such as intestinal blockage.

Once diagnosed, it’s important to treat C. diff as quickly as possible to prevent complications. Except in special situations, the antibiotic that precipitated the infection should be discontinued immediately. If you still need antibiotics to treat the original infection, other options may be available.