Diagnosis of IBS

Irritable bowel syndrome is difficult to diagnose. In most cases, test results do not show anything out of the ordinary. The intestines (bowels) often look normal, but the patient still has symptoms. Health care providers usually diagnose IBS through a process of elimination, by ruling out other diseases that cause similar symptoms (e.g., diverticulitis).

The first step in diagnosing IBS is a thorough analysis of the patient's medical history. Physicians evaluate the symptoms; the length, severity, and frequency of the symptoms; and any triggers.

For a diagnosis of IBS, symptoms must be present for 12 weeks, but those weeks need not be consecutive. At least two of the following criteria must be present:

  • Bloating and/or abdominal cramping
  • Bowel movements that occur more or less frequently and/or a change in the appearance of the stool
  • Mucus in the stool
  • Straining, the urgent need to have a bowel movement, or the feeling that the bowel hasn’t emptied

Diagnostic tests may be performed to rule out other conditions that might be causing symptoms (e.g., colon cancer, diverticulitis, inflammation of the intestines).

A colonoscopy allows the physician to examine the entire colon (large intestine) and check for abnormal features using a flexible tube with a tiny camera attached. A flexible sigmoidoscopy is a similar procedure that focuses on the lower part of the colon (called the sigmoid colon).

Stool sample tests can be used to detect infection and a hemoccult test can detect hidden blood in the stool. Blood tests can indicate celiac disease, which complicates the digestion of gluten, a wheat protein.

Imaging tests (e.g., x-rays, computed tomography [CT scan]) can be used to examine the abdomen and pelvis and detect tumors or other conditions (e.g., diverticular disease).

Lactose intolerance tests can be used to evaluate the patient's reaction to dairy products. Physicians may suggest avoiding dairy products for a few weeks to see if symptoms improve. In some cases, a psychological evaluation is performed to determine if stress is aggravating the condition.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 28 Feb 2008

Last Modified: 22 Sep 2015