Diagnosis of Irritable Bowel Syndrome
There is no specific laboratory or imaging test which can be performed to diagnose irritable bowel syndrome. Diagnosis of IBS involves excluding conditions which produce IBS-like symptoms, and then following a procedure to categorize the patient's symptoms.
Different Diagnosis
Because there are many causes of diarrhea that give IBS-like symptoms, the American Gastroenterological Association has published a set of guidelines for tests to be performed to rule out other causes for these symptoms. These include gastrointestinal infections, lactose intolerance and Coeliac disease. Research has suggested that these guidelines are not always followed. Once other causes have been excluded, the diagnosis of IBS is performed using a diagnostic algorithm. Well-known algorithms include the Manning Criteria, the obsolete Rome I and II criteria, the Kruis Criteria, and studies have compared their reliability. The more recent Rome III Process was published in 2006. Physicians may choose to use one of these guidelines, or may simply choose to rely on their own anecdotal experience with past patients. The algorithm may include additional tests to guard against mis-diagnosis of other diseases as IBS. Such "red flag" symptoms may include weight loss, GI bleeding, anemia, or nocturnal symptoms. However, researchers have noted that red flag conditions may not always contribute to accuracy in diagnosis — for instance, as many as 31% of IBS patients have blood in their stool.
The diagnostic algorithm identifies a name which can be applied to the patient's condition based on the combination of the patient's symptoms of diarrhea, abdominal pain, and constipation. For example, the statement "50% of returning travelers had developed functional diarrhea while 25% had developed IBS" would mean that half the travelers had diarrhea while a quarter had diarrhea with abdominal pain. While some researchers believe this categorization system will help physicians understand IBS, others have questioned the value of the system and suggested that all IBS patients have the same underlying disease but with different symptoms.
Misdiagnosis
Published research has demonstrated that some poor patient outcomes are due to treatable causes of diarrhea being mis-diagnosed as IBS. Common examples include infectious diseases, celiac disease, helicobacter pylori, parasites, food allergies (though considered controversial), and lactose intolerance.
Celiac disease in particular is often misdiagnosed as IBS. The American College of Gastroenterology recommends that all patients with symptoms of IBS be tested for celiac disease. Chronic use of certain sedative-hypnotic drugs especially the benzodiazepines may cause irritable bowel like symptoms which can lead to a misdiagnosis of irritable bowel syndrome.
