Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome (IBS) can be diagnosed based on symptoms. In most cases, only minimal tests are needed. A health professional diagnoses IBS when a person has the typical symptoms of the disorder and, if needed, tests have ruled out other possible causes.

The amount of testing that may be done depends on several factors: your age, how your symptoms come on and how severe they are, and how you respond to the initial treatment. For example:

• For a 20-year-old woman who has all the typical symptoms of IBS, a routine blood test may be the only test needed. Irritable bowel syndrome is more common in young women, and so if symptoms are typical of IBS, extensive testing is probably not needed.
• For a 55-year-old man whose symptoms started recently, more extensive testing is probably needed. People over age 50 are less likely than younger people to develop IBS symptoms for the first time, so it is more likely that symptoms may be caused by another problem.
• If you get better after some initial treatment for symptoms that the health professional suspects are caused by IBS, no further tests are needed.

Depending on your symptoms, results of the initial tests, or your response to treatment, other tests may be done.

Should I have testing done for irritable bowel syndrome?

Tests may include:

• Medical history and physical examination.
• Complete blood count (CBC), which provides information about the kinds and numbers of red blood cells, white blood cells, and platelets in the blood; and sedimentation rate, which checks for inflammation in the body.
• Stool analysis, which may include testing for blood in the stool (fecal occult blood test), infection (stool culture), or parasites (ova and parasites test).
• Flexible sigmoidoscopy, which allows a health professional to look inside the lower part of the large intestine for abnormal growths (such as tumors or polyps), inflammation, bleeding, hemorrhoids, and other conditions (such as diverticulosis).
• Colonoscopy, which allows a doctor to look at the lining of the entire large intestine (rectum and colon) through a thin, flexible viewing instrument called a colonoscope. The colonoscope helps the doctor detect polyps, tumors, and areas of inflammation or bleeding.

Thyroid function tests are occasionally done.

In some cases, treatment with diet or medicines may not help. If diarrhea is the main symptom and it is not getting any better, a blood test for celiac disease may be done. Celiac disease is a lifelong (chronic) condition in which foods that contain gluten—a form of protein found in some grains, notably wheat, barley, and rye—damage the small intestine, making it unable to properly absorb nutrients. Celiac disease may cause symptoms similar to IBS symptoms.

If the diagnosis is unclear after routine tests and you have other symptoms or pain in an area of the abdomen that may indicate a different problem, further tests may be done to clarify the diagnosis. These tests may include:

• Upper endoscopy, which allows your doctor to look at the lining of your esophagus, stomach, and the first part of your small intestine (duodenum) through a thin, flexible viewing instrument called an endoscope. The endoscope helps your doctor look for ulcers, inflammation, tumors, infection, or bleeding.
• Upper gastrointestinal (UGI) series, which examines the upper and part of the middle portions of the digestive tract. After you swallow a "shake" made of barium and water, X-rays are taken to track the movement of the barium through the esophagus, stomach, and first part of the small intestine (duodenum) using fluoroscopy connected to a video monitor.
• Gallbladder ultrasound, which can provide a picture of the gallbladder.
• Barium enema, an X-ray examination of the large intestine (colon and rectum) or small intestine.

If results of the above tests don't show any clear problem, further testing, such as an abdominal computed tomography (CT) scan may be needed to check for inflammatory bowel disease or other problems. These tests are not discussed here. For more information, see the topic Crohn's Disease or Ulcerative Colitis, two major types of inflammatory bowel disease.