IBS Testing and Diagnosis

Irritable bowel syndrome (IBS) stems from a problematic relationship between the gut and the brain. IBS can be hard to diagnose because it does not have a clear cause. It also may have different causes and symptoms in different people.¹

By definition, a syndrome is a set of symptoms that occur together. Doctors typically diagnose IBS based on a person’s symptoms and the pattern they occur in. But IBS has symptoms in common with many other gastrointestinal (GI) disorders. Doctors may perform certain tests to rule out these other disorders before diagnosing IBS.^2,3

Symptoms of IBS

The most common symptoms of IBS are belly (abdominal) pain, diarrhea, and constipation. Most people with IBS have belly pain, but some people have only diarrhea or only constipation. Some people have both diarrhea and constipation.¹

Along with these primary symptoms, IBS also can cause:¹

• Gas and bloating
• Feeling like you cannot complete a bowel movement
• Passing mucus with your stool

Medical history and physical exam

Your primary care doctor or a gastroenterologist (doctor who specializes in digestive disorders) can diagnose IBS. First, your doctor will take a complete medical history. This includes asking about your family health history. Having a family member with IBS or other GI disorder may make you more likely to have IBS.^2-4

Your doctor also will ask about your personal health history, including:^2,3

• Past and current symptoms, when they started, and how often they occur
• Other health conditions, including any mental health challenges
• Any history of GI infections
• What medicines you take
• The type of diet you eat
• Travel history
• Any life stress or trauma that may be linked to your gut symptoms

After gathering health history information, your doctor will perform a physical exam. They may press or tap on your abdomen to check for pain or bloating. They also may listen to your gut with a stethoscope. And they might look at your rectum to see whether there is any blood in your stool.²

Diagnostic criteria for IBS

Your doctor will likely use a certain set of guidelines called the Rome IV criteria to decide whether your symptoms qualify as IBS. According to these guidelines, you have IBS if the following is true of your symptoms:⁵

• Your symptoms started at least 6 months ago
• In the last 3 months, you have had abdominal pain at least 1 day per week
• The abdominal pain was related to at least 2 of the following:
• Having a bowel movement
• A change in how often you had bowel movements
• A change in the way your stool looked

If your doctor diagnoses you with IBS, they will assign it a type. Your type of IBS is based on your primary symptom on days that you have an abnormal bowel movement. Your type may determine the right treatment for you. The 3 types of IBS are:⁵

• IBS with diarrhea (IBS-D) – More than one-fourth of your stools are loose and watery
• IBS with constipation (IBS-C) – More than one-fourth of your stools are hard and lumpy
• IBS with mixed bowel habits (IBS-M) – More than one-fourth of your stools are loose and watery, AND more than one-fourth of your stools are hard and lumpy

Diagnostic tests

Doctors do not need to perform any tests to diagnose IBS. But they may want to run certain tests to make sure your symptoms are not caused by another health condition. Serious conditions that can cause similar symptoms as IBS include:³

• Inflammatory bowel disease (IBD)
• Celiac disease
• Gut infections
• Nerve (neurological) conditions like multiple sclerosis or Parkinson’s disease
• Diabetes
• Endometriosis
• Cancer

To rule out these and other possible causes of your symptoms, your doctor may want to perform other tests, such as:^2,6

• Blood tests – These lab tests can detect signs of infection, anemia, cancer, or inflammation that may point to other GI conditions.
• Stool tests – Analyzing your poop can help doctors find signs of infection, parasites, problems with your body’s ability to absorb nutrients (malabsorption), or other GI problems.
• Colonoscopy or endoscopy – These procedures can help diagnose or rule out IBD, colon cancer, and celiac disease. During the procedure, your doctor will insert a scope with a camera on it to look inside your digestive tract. They may also take a small tissue sample to look at later under a microscope (biopsy).
• Computed tomography (CT) scan – This imaging test can help your doctor detect other causes of belly pain.
• Breath tests – Measuring the chemical makeup of your breath can help doctors rule out lactose intolerance and small intestinal bacterial overgrowth (SIBO). Lactose intolerance means you cannot digest the sugar in dairy products. SIBO means you have too much of certain bacteria in your small intestine, which can lead to symptoms like gas, bloating, and diarrhea.

When to contact your doctor

IBS may affect as many as 15 percent of people, but most people with IBS do not get medical care for it. While IBS does not damage your body, its symptoms can be very uncomfortable and lower your quality of life. Treatment may help relieve some of these symptoms.^1,3

Certain symptoms may be signs of a serious medical condition that is not IBS. Contact your doctor right away if you have any of the following:^2,6

• Symptoms that begin after age 50 (because IBS is less common, and cancer is more common, in older people)
• Unexplained weight loss
• Bleeding from your rectum or bloody, black, or tarry stools
• Long-term nausea, vomiting, or diarrhea
• Diarrhea or abdominal pain that wakes you up at night
• Abdominal pain that is not related to a bowel movement
• Fever