Tests

Doctors typically diagnose irritable bowel syndrome after ruling out other, more serious diseases, such as ulcerative colitis or colon cancer. This involves first taking the patient's medical history, including a description of the troubling symptoms. If a patient is experiencing some of the following "alarm symptoms" and is older than 50 years, then more extensive testing should be done to rule out a more serious illness. Alarm symptoms include unexplained weight loss, anemia, fever, evidence of bleeding in the digestive tract, persistent or worsening pain, family history of colon cancer, and diarrhea, which occurs even when no food is eaten, which occurs at night, or is of a large volume. A physical exam comes next, followed by any necessary laboratory tests.

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Tests commonly ordered to figure out if someone has IBS include:

• Analysis of a stool sample to check for evidence of bleeding.
• Blood tests to rule out other illnesses, including a complete blood count, blood chemistry panel, and a test that's used to monitor inflammatory disease.

The doctor may also order X-rays of the abdomen, such as a standard X-ray, a barium test, or a CT scan, or an endoscopic exam of the lower gastrointestinal tract, in which a flexible tube is inserted to look at the lower part of the colon.

If a patient is over 50, the doctor may decide to do a colonoscopy, which uses a flexible scope to examine the entire colon. This test is used to look for colon cancer, as well as for precancerous polyps that can cause bleeding.

If the tests come back negative, meaning the person is healthy aside from IBS symptoms, the doctor may diagnose IBS if the following criteria apply:

• Abdominal pain or discomfort has been present for at least 12 weeks out of the past 12 months. These weeks do not have to be consecutive.
• The abdominal pain or discomfort has at least two of these three features: It is relieved by having a bowel movement; the frequency of bowel movements changes when discomfort starts; or there is a change in the way the stool looks when discomfort starts.