How is IBS diagnosed?
Clinicians diagnose IBS by identifying typical symptoms, taking a thorough history and doing a complete physical examination, and testing blood samples for other potential causes of symptoms. Stool tests are also indicated as a means of testing for minute amounts of blood in the stools (occult blood), and sometimes to exclude active infection as the cause of symptoms.
In some patients, examining the colon with colonoscopy may be indicated, particularly for anyone 50 or over. The most important organic diseases that can have similar symptoms are inflammatory bowel disease, colon cancer, celiac disease, and in women, ovarian cancer, which can initially present simply as abdominal bloating.
Signs and symptoms that suggest organic disease, rather than IBS, are onset of symptoms over age 50, short duration of symptoms, blood in the stools, symptoms waking one at night, unintentional weight loss, anemia, fever, mass on rectal or abdominal exam, symptoms associated with recent antibiotics, and a family history of organic GI disease (such as colon cancer, inflammatory bowel disease, and celiac disease). If one or more of these features is present, further clinical investigation is indicated.