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Colitis (cont.)

What Exams and Tests Diagnose Colitis?

While unpleasant, the rectal examination is very important. Using a finger, the doctor feels inside the rectum, exploring for any masses or tumors. The color and consistency of stool can be evaluated, and if it is not grossly bloody, can be tested for occult blood (blood that is present but cannot be seen with the naked eye).

Laboratory Tests

The history will assist the health-care professional decide the tests to order and what cultures would be appropriate. Blood tests help assess the stability of the patient, and also explore any potential issues associated with colitis.

  • A complete blood count (CBC) will assess the red blood cell count, the white blood cell count, and the number of platelets.
    • The red blood cell count will help define the amount of bleeding.
    • White blood cell counts elevate when the body is undergoing physical (exercise), physiological, or emotional stress.
    • Platelets help blood to clot, so knowing the platelet number in a patient with bleeding may be useful.
  • Electrolyte abnormalities can occur with diarrhea. Low sodium (hyponatremia) and low potassium (hypokalemia) levels may occur and cause symptoms far removed from the initial colitis signs and symptoms.
  • Kidney function may be assessed by measuring the BUN (blood urea nitrogen) and creatinine levels.
  • Erythrocyte sedimentation rate (ESR) and C reactive protein (CRP) are nonspecific test of inflammation in the body.
  • Stool samples may be collected for culture, looking for infection as the cause of colitis


If a specific cause of colitis is not readily apparent, then colonoscopy may be considered. A gastroenterologist will insert a long flexible fiberoptic camera into the anus and examine the full length of the colon. The appearance of the colon by itself may be enough to make the diagnosis. Biopsies (small pieces of tissue) may be taken from the lining of the colon and examined by a pathologist (a medical doctor specializing in the diagnosis of tissues) to help confirm the diagnosis. Microscopic colitis (lymphocytic and collagenous) can only be diagnosed with biopsy of the affected area.

Colonoscopy is an essential cancer screening test and is especially important for those patients who have had blood in their stool that cannot be explained by another diagnosis.


Computerized tomography (CT) may be used to image the colon and the rest of the abdomen. Different types of colitis have distinctive patterns that may help a radiologist recognize a specific diagnosis. A CT scan may be ordered urgently if the history and physical examination performed by the health-care professional leads to concern that an urgent or emergent problem exists that might require surgery. On occasion, a barium enema or other imaging tests such as ultrasound may be used to evaluate the anatomy of the colon and assist in diagnosis.

Last Reviewed 11/20/2017

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Read What Your Physician is Reading on Medscape

Colitis »

Colitis is an inflammation of the colon. It may be associated with enteritis (inflammation of the intestine) and/or proctitis (inflammation of the rectum).

Read More on Medscape Reference »

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