Diagnosing irritable bowel syndrome isn’t like diagnosing other diseases. Your doctor can’t take a swab or a vial of blood and test it to determine the problem. There is no single test that can point to IBS as the cause of your symptoms.
Instead, when you go to your doctor about IBS symptoms like diarrhea, constipation, abdominal pain, and stomach cramps, he has to rule out other conditions and then pay careful attention to your symptoms before giving you a diagnosis.
Diagnosing IBS “For years, anyone who had gastrointestinal symptoms that couldn’t be explained was told they had IBS,” says Steven Field, MD, a gastroenterologist and clinical assistant professor of medicine at New York University School of Medicine in New York City. But now doctors use the "Rome criteria," which are a specific set of symptoms that have to be present in order to give a diagnosis. In addition, the criteria designate red-flag symptoms that don’t point to IBS, he says.
Giving your doctor detailed information about your symptoms and when you experience them will go a long way toward getting an accurate diagnosis. Here’s what your doctor considers before he makes a diagnosis:
Laboratory tests to rule out other conditions. To make sure something other than IBS isn’t causing your symptoms, your doctor may run blood tests, test your stool sample, order an X-ray, or perform a colonoscopy (a procedure in which your doctor uses a small flexible camera to look inside your colon).
Your symptoms. Under the Rome criteria, a diagnosis of IBS can be made if you have had abdominal pain during at least 12 weeks during a 12-month period, even if those 12 weeks aren’t consecutive, and if you experience two of these three things:
- A bowel movement that causes the abdominal pain to go away
- A change in the frequency of your bowel movements
- A change in your stool’s appearance (it becomes hard and lumpy or loose and watery
Other signs of IBS include mucus in your stool, a swollen abdomen, an urgency to have a bowel movement, having trouble passing stool, or a feeling that your bowel isn’t empty after going to the bathroom.
If you have red flag symptoms. Your doctor will also be looking for red-flag symptoms that aren’t associated with IBS, Dr. Field says. Those include:
- Blood in your stool
- Unexplained weight loss
- Pain or diarrhea that’s so intense it wakes you up when you’re asleep
- What triggers your symptoms. The factors that bring on your symptoms are another clue as to whether or not you have IBS. Eating such items as fried and greasy foods, caffeine, dairy products, chocolate, alcohol, and carbonated drinks often trigger symptoms, but the exact food triggers are different for everyone. Large meals may also trigger IBS symptoms.
Stress — which can result from major life changes such as getting married or getting a new job — is also a major trigger for IBS symptoms, Field says. And for women, symptoms are usually more severe during their menstrual period, possibly because of the effect of hormones on IBS.
The bottom line: Giving your doctor detailed information about your symptoms and knowing what triggers them will help with your diagnosis. Many doctors recommend keeping a food diary to determine exactly what brings on your symptoms and sharing that information with your doctor to make a better diagnosis and get you the right treatment.
By Marie Suszynski | Medically reviewed by Cynthia Haines, MD