Diagnosis of IBS

The Diagnosis of a functional bowel disorder always presumes the absence of a structural or biochemical explanation for the symptoms. A diagnostic test for IBS via assessment of colonic/rectal hypersensitivity using a barostat is currently being discussed.

Diagnostic Testing
Testing is depends on factors such as age, sex, family history of gastrointestinal disease, presence of stress or other psychological factors, specific symptom predominance, symptom duration and severity, presence of non-IBS symptoms, and test availability and cost.

The tests that are especially relevant to the evaluation of IBS symptoms include
Blood Tests - A complete blood count is often done to check for anemia and other abnormalities. Other tests may be performed, including an erythrocyte sedimentation rate [indicates if tissue damage or inflammation is present] and a thyroid test.

Stool Tests - The most common fecal examinations check for an intestinal parasite or occult (hidden) blood in the stool.

Sigmoidoscopy or Colonoscopy - These direct visual examinations of the rectum and sigmoid portion of the large bowel (sigmoidoscopy) or the entire large bowel (colonoscopy) are performed with an endoscope. (See IFFGD Fact Sheet No. 114 for further information on these procedures.)

Barium Enema - This is a radiologic (x-ray) examination of the large bowel that is performed by taking x-ray pictures of the bowel after it has been distended with a barium-containing liquid and air. The amount of radiation involved is usually not worrisome, but women who are pregnant or unsure whether they are pregnant should tell their physician, as this test should not be done in such cases.

Psychological Tests - Questionnaires that detect anxiety, depression or other psychological problems may be used to supplement the evaluation routinely or applied in special circumstances.

Miscellaneous Tests - Other tests may be done depending on specific aspects of a patient's illness, especially atypical symptoms or alarm signs. Radiologic examination of the small intestine performed after the patient drinks a barium preparation can exclude disease in that organ. Lactose tolerance testing (usually by a breath test) can identify deficiency of lactase, the intestinal enzyme necessary for digestion of the milk sugar, lactose. Anorectal manometry (measurement of the neuromuscular function of the anus) is used in certain patients with predominant constipation or fecal incontinence, and colon transit (content movement) studies are sometimes done. However, many patients do not require these or other miscellaneous tests.