If you suspect you have a clostridium 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.

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.

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:

  • Enzyme immunoassay. Most labs use the enzyme immunoassay (EIA) test, which is faster than other tests, but isn’t sensitive enough to detect many infections and has a higher rate of falsely normal tests.
  • Polymerase chain reaction. This sensitive molecular test can rapidly detect the C. difficile toxin B gene in a stool sample and is highly accurate. It’s now being adapted by several laboratories and becoming more widely available.
  • 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, more cumbersome to do and requires more than 24 to 48 hours for test results. Some hospitals use both the EIA test and cell cytotoxicity assay to ensure accurate results.

Testing for C. diff is unnecessary if you’re not having diarrhea or watery stools.

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.

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.


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.