How Irritable Bowel Syndrome (IBS) Is Diagnosed

Diagnosing irritable bowel syndrome (IBS) can often be about confirming what you don't have, as much as it is about confirming you meet the diagnostic criteria for IBS.

As a functional gastrointestinal disorder, there isn't any identified structural or tissue problem. Rather, IBS is a problem of function, specifically of bowel function.

IBS is a chronic condition that causes abdominal pain and abnormal stools—symptoms that are consistent with many other gastrointestinal issues. Many of the tests that your doctor orders, including blood work and imaging, will help to rule out other gastrointestinal problems. By doing so, your IBS diagnosis is more conclusive.

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Self-Checks

There is no way for you to definitively determine if you have IBS yourself, which is why it is highly recommended that you make an appointment with your primary care physician if you are experiencing recurrent symptoms.

It's helpful to start keeping a simple food and symptom diary, so you have a log of exactly what you've been experiencing and for how long.

Keep track of what you eat and when, and how your body responds. Additionally, record when you have pain, diarrhea, and/or constipation. You may also want to record stressors, because of the connection of the gut with your brain.

You should log any other symptoms you experience like bloating, flatulence (gas), and acid reflux. Even symptoms like fatigue, headaches, heart palpitations, and bladder urgency should be recorded, especially if you consistently experience them along with the more obvious IBS symptoms.

The information you record might help your provider to make a diagnosis. You can use our Doctor Discussion Guide below to help you talk about your symptoms with a professional.

IBS Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Man

A "Positive Diagnostic Strategy"

In their 2021 clinical guidelines for IBS, the American College of Gastroenterology (ACG) recommends "a positive diagnostic strategy" instead of diagnosing IBS by ruling out other diagnoses (a "diagnostic strategy of exclusion").

That means that people should be a given a physical exam, some lab tests, and minimal diagnostic testing if they present with abdominal pain and altered bowel habits that have lasted more than six months. The caveat? Certain "alarm features" need more testing to rule out more serious problems.

"Alarm features" include:

The ACG argues that much time and money could be saved by following the Rome IV diagnostic criteria, subtyping the person with IBS-C, IBS-D, IBS-M or IBS-U, and performing appropriate tests as the indication arises. This would also allow patients to start appropriate treatment as soon as possible, increasing patient satisfaction.

A research study of 302 people found that there was no advantage in unnecessary diagnostic testing, and a "positive diagnostic approach" was just as accurate as performing a battery of tests.

Rome IV Criteria

Because IBS is considered a functional disorder, in that there is no visible disease process, physicians often use the Rome IV ("Rome 4") criteria to diagnose IBS.

According to these criteria, IBS is diagnosed if symptoms have been present at least one day per week during the last three months and started six or more months ago.

Symptoms must consist of recurrent abdominal pain with two or more of the following being true:

  • Pain is related in time to a bowel movement.
  • Onset of pain is related to a change in frequency of stool.
  • Onset of pain is related to a change in the appearance of stool.

While the Rome IV Criteria is a helpful resource, many primary care doctors prefer that a more thorough investigation be done and may refer you to a gastroenterologist.

Gastroenterologists use their knowledge of the workings of the entire digestive system and their experience in the various disorders of the gastrointestinal system to come up with a comprehensive diagnosis and treatment plan.

Physical Exam and Lab Tests for IBS

So that you get the proper treatment, the ACG recommends that certain disorders be ruled out. To do that, they recommend:

  • Blood tests to rule out celiac disease, if you are having diarrhea
  • Fecal testing and a blood test called a C-reactive protein (CRP) to rule out inflammatory bowel disease in people suspected of having IBS with diarrhea
  • Testing for parasites like Giardia only if there has been travel to poor areas, camping, daycare exposure, or exposure to poor water quality
  • Testing for food allergies and sensitivities only if there is a consistent and reproducible effect from eating a certain food
  • Anorectal physiology testing to rule out dyssynergic defecation (DD), particularly if constipation does not respond to treatment or if a pelvic floor disorder is suspected

Imaging

Should your symptoms or family medical history warrant it, your doctor might recommend additional testing to be sure that you do not have another condition that mimics IBS, such as inflammatory bowel disease (IBD) or colon polyps.

If this happens, they may recommend one of these other common gastrointestinal procedures:

  • Colonoscopy: A scope of your entire large intestine
  • Sigmoidoscopy: Examination of the rectum and the lowest part of the colon, called the sigmoid colon
  • Upper endoscopy: A scope of your upper digestive tract, including your esophagus, stomach, and duodenum
  • Lower GI series (barium enema): X-ray of the large intestine with barium used for contrast
  • Upper GI series: X-rays of the upper digestive system with barium used for contrast

Once certain conditions have been ruled out and the criteria of the Rome IV criteria are met, your doctor can confidently diagnose you as having IBS.

Differential Diagnoses

There are a number of common digestive health problems that share some of the same symptoms as IBS. For instance, celiac disease (an autoimmune response to eating gluten) and food intolerances (gastrointestinal responses to certain foods) often have symptoms that are similar to IBS.

Meanwhile, IBD (Crohn's disease and ulcerative colitis) and colon cancer can also share some symptoms. The difference is that people with these diseases many times experience rectal bleeding or other "alarm signs" listed above, in addition to abdominal pain, gas, bloating, diarrhea, and constipation. People with IBS usually do not have rectal bleeding unless it is from hemorrhoids.

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