IBS—or irritable bowel syndrome—is one of the most common conditions in the world, yet doctors and patients alike are still confounded by what causes it and the best way to manage it. Ultimately, it’s only definition is its symptoms.
“IBS is a description of symptoms that affect patients—generally it’s abdominal pain associated with alternating diarrhea or constipation,” says Benjamin Cohen, MD, gastroenterologist at The Mount Sinai Hospital in New York City. Learn more about IBS symptoms here.
Because IBS doesn’t cause any noticeable damage or changes to the digestive tract, it can also be tough for doctors to diagnose it. Think of it this way: For a condition like ulcerative colitis, you would find inflammation and ulcers in the lining of the colon. For strep throat, you would test positive for the Streptococcal bacteria. For cervical cancer, abnormal cell changes would appear in your Pap smear.
IBS doesn’t have any test like that. Because IBS is so common, many doctors can recognize the textbook symptoms of IBS when a patient comes to them; however, many other conditions can cause similar tummy symptoms—like inflammatory bowel disease, celiac disease, lactose intolerance, or even colon cancer—and doctors have to find a way to be confident in their IBS diagnosis.
“IBS is a diagnosis of exclusion, so in order to label somebody as having IBS, you have to rule out other organic causes of their symptoms,” says Dr. Cohen. “Only after you’ve shown that it’s not any of those things can you say that the symptoms are irritable bowel syndrome.”
To rule out other related conditions, doctors often do the following tests before making an IBS diagnosis:
Colonoscopy: This exam of the large intestine checks for problems like inflammation, ulcers, and polyps. A “normal” large intestine could suggest IBS.
Upper endoscopy: This exam checks for problems in the esophagus, stomach, and start of the small intestine. If these all appear “normal,” the patient might have IBS.
Cross-sectional imaging (CT scan or MRI): This can check for tumors or lumps in organs like your stomach.
Manometry: This checks the motility of your food as it digests by watching the strength and coordination of your GI tract as it pushes food through. This can catch motility issues that might explain symptoms.
Blood work: This can reveal changes in inflammatory markers, or antibodies that may indicate celiac disease, for example. No evidence of inflammation may suggest IBS.
Fecal test: An examination of fecal matter can reveal many things: inflammation, infection (such as food poisoning), or lactose intolerance and celiac disease (both of which can change the quality of poop).
If you suspect you may have IBS, you won’t get all of these tests done the first time you head to your doctor. These may be spread out over days, weeks, or even months, and you likely won’t need all of the tests.
“The first visit is really getting a detailed history, and it’s important for patients to come in with [a] clear timeline of their symptoms and potential triggers,” says Dr. Cohen.
Overview of colonoscopy in adults. Waltham, MA: UpToDate, 2019. (Accessed on December15, 2021 at https://www.uptodate.com/contents/overview-of-colonoscopy-in-adults.)
Overview of gastrointestinal motility testing. Waltham, MA: UpToDate, 2019. (Accessed on December15, 2021 at https://www.uptodate.com/contents/overview-of-gastrointestinal-motility-testing.)
Overview of upper gastrointestinal endoscopy (esophagogastroduodenoscopy). Waltham, MA: UpToDate, 2019. (Accessed onDecember15, 2021 at https://www.uptodate.com/contents/overview-of-upper-gastrointestinal-endoscopy-esophagogastroduodenoscopy.)
Patient education: irritable bowel syndrome (beyond the basics). Waltham, MA: UpToDate, 2019. (Accessed on December15, 2021 at https://www.uptodate.com/contents/irritable-bowel-syndrome-beyond-the-basics.)