• Diagnosis of Irritable Bowel Syndrome (IBS)

    The diagnosis of IBS is one of exclusion. This means that a firm diagnosis cannot be made until all other causes of 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, colon or rectal cancers, or infectious disease.
    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 2 or more of the following symptoms at least 3 days a month during the preceding 3 months:
    • Pain relieved by a bowel movement
    • 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—To look for causes of infection.
    • Blood and urine tests
    • Barium enema—Constrast material is inserted into the rectum. The contrast makes colorectal structures and any abnormalities easier to see.
    • Sigmoidoscopy—A lighted tube with a camera is inserted through the rectum to examine the rectum and the lower part of the colon. If needed, tissue samples (biopsy) can be taken for examination under a microscope.
    • Colonoscopy —A lighted tube with a camera is inserted through the rectum to examine the rectum and the entire length of the colon. If needed, tissue samples (biopsy) can be taken for examination under a microscope.
    Copyright © Nucleus Medical Media, Inc.
    Copyright © Nucleus Medical Media, Inc.
    Other test may include:
    • Absorption tests—To evaluate the food digestion process. This will determine if food is absorbed properly or if it is passing through the gastrointestinal tract without absorption.
    • X-rays of the stomach or gallbladder.
    • Hydrogen breath test—To look for bacterial overgrowth.


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

    IBS. American Gastroenterological Association website. Available at: http://www.gastro.org/patient-care/conditions-diseases/irritable-bowel-syndrome. Accessed December 18, 2015.

    Irritable bowel syndrome (IBS). EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated September 1, 2015. Accessed December 18, 2015.

    Irritable bowel syndrome (IBS). Merck Manual Professional Version website. Available at: http://www.merckmanuals.com/professional/gastrointestinal-disorders/irritable-bowel-syndrome--(ibs)/irritable-bowel-syndrome--(ibs). Updated July 2013. Accessed December 18, 2015.

    Irritable bowel syndrome diagnosis. Irritable Bowel Syndrome Self-help and Support Group website. Available at: http://www.ibsgroup.org/diagnosis. Accessed December 18, 2015.

    Pimentel M, Park S, Mirocha J, Kane SV, Kong Y. 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.

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