Diagnosis

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, ibuprofen (Advil, Motrin IB, others), naproxen sodium (Aleve), proton pump inhibitors, and selective serotonin reuptake inhibitors (SSRIs) — which may increase your risk of microscopic colitis.

Tests

To help confirm a diagnosis of microscopic colitis, you may have one or more of the following tests and procedures:

• Colonoscopy. This exam allows your doctor to view your entire colon using a thin, flexible, lighted tube (colonoscope) with an attached camera. The camera sends images of your rectum and entire colon to an external monitor, allowing your doctor to examine the intestinal lining. The doctor can also insert instruments through the tube to take a tissue sample (biopsy).

• Flexible sigmoidoscopy. This procedure is similar to a colonoscopy, but rather than viewing the entire colon, a flexible sigmoidoscopy allows your doctor to view the inside of the rectum and most of the sigmoid colon — about the last 2 feet (61 centimeters) of the large intestine.

  The doctor uses a slender, flexible, lighted tube (sigmoidoscope) to examine the intestinal lining. A tissue sample can be taken through the scope during the exam.

Because intestinal issues often appear normal in microscopic colitis, a definite diagnosis of microscopic colitis requires a colon tissue sample (biopsy) obtained during a colonoscopy or flexible sigmoidoscopy. In both subtypes of microscopic colitis, cells in colon tissue have a distinct appearance under the microscope, so the diagnosis is definite.

Additional testing

In addition to a 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.