Tests and diagnosis

By Mayo Clinic Staff

A diagnosis of irritable bowel syndrome depends largely on a complete medical history and physical exam.

Criteria for making a diagnosis

Because there are usually no physical signs to definitively diagnose irritable bowel syndrome, diagnosis is often a process of elimination. To help in this process, researchers have developed diagnostic criteria, known as Rome criteria, for IBS and other functional gastrointestinal disorders. These are conditions in which the bowel appears normal, but doesn't function normally. According to these criteria, you must have certain signs and symptoms before a doctor diagnoses irritable bowel syndrome.

The most important symptom is:

  • Abdominal pain and discomfort lasting at least 12 weeks, though the weeks don't have to occur consecutively

You also must have at least two of the following:

  • A change in the frequency or consistency of your stool — for example, you may change from having one normal, formed stool every day to three or more loose stools daily, or you may have only one hard stool every few days
  • Straining, urgency or a feeling that you can't empty your bowels completely
  • Mucus in your stool
  • Bloating or abdominal distension

Your doctor will likely assess how you fit these criteria, as well as whether you have any other signs or symptoms that might suggest another, more-serious condition. Some red flag signs and symptoms that might prompt your doctor to do additional testing include:

  • New onset after age 50
  • Weight loss
  • Rectal bleeding
  • Fever
  • Nausea or recurrent vomiting
  • Abdominal pain, especially if it's not completely relieved by a bowel movement
  • Diarrhea that is persistent or awakens you from sleep

If you have these red flag signs or symptoms, you'll need additional testing to further assess your condition.

If you fit the IBS criteria and don't have any red flag signs or symptoms, your doctor may suggest a course of treatment without doing additional testing. But if you don't respond to that treatment, you'll likely require more tests.

Additional tests

Your doctor may recommend several tests, including stool studies to check for infection or malabsorption problems. Among the tests that you may undergo to rule out other causes for your symptoms are the following:

  • Flexible sigmoidoscopy. This test examines the lower part of the colon (sigmoid) with a flexible, lighted tube (sigmoidoscope).
  • Colonoscopy. In some cases, your doctor may perform this diagnostic test, in which a small, flexible tube is used to examine the entire length of the colon.
  • Computerized tomography (CT) scan. CT scans produce cross-sectional X-ray images of internal organs. CT scans of your abdomen and pelvis may help your doctor rule out other causes of your symptoms.
  • Lactose intolerance tests. Lactase is an enzyme you need to digest the sugar (lactose) found in dairy products. If you don't produce this enzyme, you may have problems similar to those caused by irritable bowel syndrome, including abdominal pain, gas and diarrhea. To find out if this is the cause of your symptoms, your doctor may order a breath test or ask you to exclude milk and milk products from your diet for several weeks.
  • Blood tests. Celiac disease (nontropical sprue) is sensitivity to wheat protein that also may cause signs and symptoms like those of irritable bowel syndrome. Blood tests may help rule out that disorder.
Jul. 29, 2011