A complete medical history and physical examination can help determine whether other conditions, such as celiac disease, may be contributing to your diarrhea.

Your doctor will also ask about any medications you are taking, particularly aspirin and ibuprofen (Advil, Motrin IB, others), which may increase your risk of microscopic colitis.

A definite diagnosis of microscopic colitis requires a colon tissue sample (biopsy) obtained during a colonoscopy or flexible sigmoidoscopy. Both these tests use a long, thin tube with a camera on the end and an attached tissue-sampling device to examine the inside of your colon and remove a sample of tissue. In both subtypes of microscopic colitis, cells in colon tissue have a distinct appearance under the microscope, so the diagnosis is definite.

Other tests

In addition to colonoscopy or flexible sigmoidoscopy, you may have one or more of these tests to rule out other causes for your symptoms.

  • Stool sample analysis to help rule out infection as the cause of persistent diarrhea.
  • Blood test to look for signs of anemia or infection.
  • Upper endoscopy with biopsy to rule out celiac disease. Doctors use a long, thin tube with a camera on the end to examine the upper part of your digestive tract. They may remove a tissue sample (biopsy) for analysis in the laboratory.