Despite the tendency to order diagnostic testing in the face of irritable bowel syndrome (IBS) symptoms, the diagnostic criteria for IBS, such as those supported by the Rome Committee, encourage clinicians to make a positive diagnosis on the basis of validated symptom criteria, and emphasize that IBS is not a diagnosis of exclusion, despite the extensive list of other conditions that masquerade as IBS. The current Rome guidelines for IBS state that IBS can be diagnosed in the absence of ‘alarm features,’ and is ‘often properly diagnosed without testing.’
The presence of certain red flags or “alarm signs” call for special consideration of other disorders before symptoms can be attributed to IBS. These signs include:
- Anemia and other abnormal blood tests
- New onset of symptoms at age 50 or older
- Blood in the stools
- Nighttime symptoms that awake the individual
- Unintentional weight loss
- Change in the symptom quality (e.g., new and different pain)
- Recent use of antibiotics
- A family history of other GI diseases like inflammatory bowel disease, celiac disease, or colon cancer
These signs are not automatically cause for alarm. A separate, benign problem is often found that explains them. For example, rectal bleeding may be caused by hemorrhoids, or IBS symptoms may worsen during menstrual periods.
In addition to pain and bowel dysfunction, some people with IBS suffer from other chronic functional symptoms or conditions. Each of them may require a directed diagnostic approach. These problems can include:
- Fibromyalgia (muscle aching)
- Dyspepsia (upper abdominal discomfort or pain)
- Chest pain
- Urinary or gynecological symptoms
Testing is individualized depending on factors such as family history, presence of stress factors, symptom features, and others.
The tests that are especially relevant to the evaluation of IBS symptoms may include:
Blood Tests – A complete blood count is often done to check for anemia and other abnormalities. Others include a test for tissue damage or inflammation, and a test for celiac disease.
Stool Tests – Most commonly these check for a bacterial infection, an intestinal parasite, or blood in the stool.
Sigmoidoscopy or Colonoscopy – Visual examinations of the rectum and a portion or all of the large bowel (colon) performed with a scope. Usually done when there are alarm signs such as rectal bleeding or weight loss, or as part of diagnostic screening for colon cancer after age 50.
Barium Enema – Examines the large bowel, after being coated with barium, performed by taking x-rays. This test has for the most part been replaced by colonoscopy. 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.
Miscellaneous Tests – Other tests may be done depending on specific aspects of an individual’s illness, especially atypical symptoms or alarm signs. However, many people do not require these other tests.
|Anorectal manometry||To measure the function of muscles and nerves of the anus and rectum|
|Blood biomarker profile||To distinguish IBS from other medical disorders. This test is available but requires refinement to achieve sufficient accuracy for routine screening evaluation|
|Capsule endoscopy||An accurate way to detect Crohn’s disease or other abnormalities of the small intestine|
|Colonic Transit||To measure the rate of movement of contents in the colon|
|Hydrogen Breath test||To detect lactase deficiency (lactose intolerance)|
|Lactulose/glucose breath test||To detect bacterial overgrowth syndrome|
|Upper GI X-ray (barium)|
There currently is no consistent biological marker of IBS that can be tested to make the diagnosis. Research interest is underway to find a biological marker, or set of markers. They include the use of a blood test, stool sample, or tissue sample from the colon. These would enhance the diagnostic accuracy of symptom criteria.
What if the test results are negative?
If you have the typical symptoms of IBS, and your doctor says, “Your tests are negative” it means that you don’t have some other disease. Tests look for other things, not for IBS. At this point your doctor might also say something like, “Based on your symptoms and exam, you have IBS.” Your signs and symptoms fit the standard for diagnosing IBS. The next step is to learn all you can about IBS and work with your doctor on a treatment plan that fits you. IBS is a problem with the way a system works. There is no visible evidence that shows up on a test.
That’s not the same thing as “nothing is wrong.” People have painful headaches, but nothing shows up on tests. It’s the same with IBS. What if you have a test result that is positive? It may be a minor problem. You may have something else along with your IBS, or you may have something else entirely. A doctor will help you sort this out.
Learn more about treatments for IBS
Adapted from IFFGD Publication #163 Current Approach to the Diagnosis of IBS by George F. Longstreth, MD, Chief of Gastroenterology, Kaiser Permanente Medical Plan, San Diego, CA; revised and updated by Douglas A. Drossman, MD, Co-Director UNC Center for Functional GI and Motility Disorders, University of North Carolina, Chapel Hill, NC.