The diagnosis of IBS is one of exclusion. This means that a firm diagnosis cannot be made until all other causes of your symptoms have been ruled out. This can require a rather extensive evaluation.

Your doctor will begin with questions about your symptoms and medical history, and then perform a physical and rectal exam. Several tests will be done to look for signs of other conditions such as inflammatory bowel disease , bowel cancer, infectious disease, and several other intestinal problems.

Most experts currently make the diagnosis of IBS based on the “Rome Criteria”. These criteria are largely based on the symptoms that you report. According to the Rome III Criteria, IBS can be diagnosed when you have two or more of the following symptoms at least three days a month during the preceding three months:

  • Pain relieved by defecation (having a stool)
  • Onset of symptoms with a change in stool frequency
  • Onset of symptoms with a change in stool appearance

Other symptoms such as straining, mucous, or bloating can be used to further support the diagnosis. Tests are often used to “rule out” conditions that may have similar symptoms but with more serious consequences or different treatments.

Tests may include:

Stool Guaiac —A simple test for traces of blood in the stool. It can be done at the time of your physical exam.

Stool Cultures —This involves examining a stool sample in the laboratory to look for infectious agents.

Blood and Urine Tests —These tests check for signs of more serious intestinal disease.

X-ray of the Bowel ( Barium Enema )—Barium is a dye that makes the inside of your intestines visible on an x-ray. Many conditions can be identified with this technique. You will be given instructions about how to completely empty your bowel before the test.

Sigmoidoscopy —A long, thin, lighted tube with fiberoptic vision is inserted through the rectum to examine the rectum and the lower part of your colon. This can be done in your doctor's office.

Sigmoidoscope
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Colonoscopy —A long, thin, lighted tube with fiberoptic vision is inserted through the rectum to examine the rectum and the entire colon. This may need to be done in a special procedure room.

Colonoscope
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Other Tests —These may include:

  • Biopsy of the colon—the removal of a piece of colon tissue for testing
  • Absorption tests—to help determine if food is being digested and absorbed or just passing through the intestines without being properly digested or absorbed
  • X-rays of the stomach or gall bladder
  • Blood tests, such as those to check liver, thyroid, or adrenal function. Blood work can also be used to look for celiac disease (wheat allergy).
  • Hydrogen breath testing—to help determine whether “bacterial overgrowth” is present

Revision Information

  • Reviewer: Daus Mahnke, MD
  • Review Date: 12/2013 -
  • Update Date: 01/15/2013 -
  • American Gastroenterological Association website. Available at: http://www.gastro.org . Accessed March 3, 2006.

  • Fauci AS, Braunwald E, et al. Harrison's Principles of Internal Medicine . 14th ed. New York, NY: The McGraw-Hill Companies; 2000.

  • Irritable Bowel Syndrome Self-help and Support Group website. Available at: http://www.ibsgroup.org . Accessed March 3, 2006.

  • Pimentel M, Park S, et al: The effect of a nonabsorbed oral antibiotic (rifaximin) on the symptoms of the irritable bowel syndrome: a randomized trial. Ann Intern Med . 2006;145(8):557-563.

  • Rome Foundation. Guidelines—Rome III Diagnostic Criteria for Functional Gastrointestinal Disorders. J Gastrointestin Liver Dis . 2006;(3):307-312.