Diagnosing Irritable Bowel Syndrome (IBS)


What is irritable bowel syndrome (IBS)?

Irritable bowel syndrome (IBS) is a health condition in which the large intestine is affected by a simultaneously occurring group of intestinal symptoms. IBS causes stomach discomfort or pain, diarrhea or constipation, and changes in stool consistency (thin, hard, soft or liquid stools). It affects an estimated 10 to 15 percent of Americans.

Irritable bowel syndrome is also known as spastic colitis, mucous colitis, irritable colon or spastic colon. Approximately only one-half of Americans who experience irritable bowel syndrome seek medical attention. IBS is sometimes difficult to diagnose due to the array of highly individualized symptoms. An IBS diagnosis is important in order to obtain appropriate treatment.

Diagnostic process

There is not a specific diagnostic test for irritable bowel syndrome. The diagnostic process begins with a physical exam and medical history. A health care professional will likely ask questions regarding stress levels, past/current infections, past/current symptoms, medications that intensify symptoms, and any family history of irritable bowel syndrome. It is important to be specific regarding the severity, duration and frequency of symptoms so a health care provider can identify patterns. Any signs or symptoms that may suggest a more serious condition, such as weight loss, rectal bleeding, fever, nausea, abdominal pain (not relieved by bowel movements), diarrhea (that interrupts sleep) or anemia, requires further testing. Oftentimes, a diagnosis of irritable bowel syndrome can be made based on symptoms. However, an elimination diet may be required to rule out any food allergies.

Possible tests

A physician may order tests if symptoms are severe, weight loss occurs, anemia is present or blood is present in the stool. These tests are not a requirement for an IBS diagnosis; however, they can eliminate the possibility of other serious conditions. Medical tests that may be ordered include, but are not limited to, the following:

  • Flexible sigmoidoscopy
    A flexible sigmoidoscopy involves a physician inserting a tiny camera attached to a thin, flexible tube into the rectum in order to examine the lower part of the colon. Preparation for a flexible sigmoidoscopy involves a liquid diet and enema. A sedative may be given before the procedure for relaxation purposes.
  • Colonoscopy
    A colonoscopy is an examination of the entire colon; a physician inserts a small camera attached to a thin, flexible tube into the rectum. A colonoscopy allows a physician to look for polyps in the large intestine and take any biopsies deemed necessary. As with flexible sigmoidoscopy, colonoscopy typically requires a liquid diet, strong laxative and sometimes an enema to prepare for testing. A mild sedative is typically administered.
  • X-rays or CT scans
    X-rays and CT scans of the pelvis and abdomen provide detailed images in order to identify any intestinal blockages and eliminate other possible causes of symptoms, such as pancreatic or gallbladder problems. The large intestine may be filled with a barium (liquid) enema that “lights up” on X-rays, providing a better view. A barium test is often called a lower GI series. As with flexible sigmoidoscopy and colonoscopy, a liquid diet and enema are required before testing.
  • Lactose intolerance test
    A lactose intolerance test checks that the body is producing lactase (an enzyme needed to digest the sugar in dairy products) properly. Lack of lactase in the body can cause symptoms similar to irritable bowel syndrome. Lactose intolerance can be diagnosed through a breath test.
  • Breath test
    In addition to testing for lactose intolerance, a breath test can also determine if an overgrowth of bacteria is present in the small intestine.
  • Upper endoscopy
    An upper endoscopy consists of a physician inserting a long, flexible tube with a tiny camera down the throat and into the esophagus. The physician inspects the upper digestive tract and obtains a tissue sample from the small intestine to identify any overgrowth of bacteria.
  • Stool sample test
    A stool sample test assesses the stool for bacteria, parasites, blood or bile acid (a digestive liquid produced in the liver). A sterile container, instructions on how to collect the stool, and where it should be sent for analysis are provided.
  • Blood count test
    A blood count test may be ordered to eliminate other health conditions; however, there is no definitive blood laboratory test for irritable bowel syndrome. A blood test can help confirm IBS if the main symptom is diarrhea; however, the test results are often inconclusive. A possible IBS-D (irritable bowel syndrome with diarrhea) diagnosis is usually accompanied by testing for celiac disease (gluten intolerance).

Diagnostic criteria

When the possibility of other health conditions is eliminated, an appropriate treatment plan will then be determined by using a set of diagnositic criteria:

  • Rome criteria
    Abdominal pain and discomfort lasts at least one day per week in the past three months and includes at least two of the following: pain or discomfort related to defecation, altered defecation frequency and altered stool consistency.
  • Manning criteria
    Pain is relieved after a complete or incomplete bowel movement, mucus is present in the stool, and stool consistency is altered.
  • Type of IBS
    Irritable bowel syndrome with constipation (IBS-C)
    Irritable bowel syndrome with diarrhea (IBS-D)
    Irritable bowel syndrome with mixed patterns of constipation and diarrhea (IBS-M)
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