IBS Testing and Diagnosis

It can be difficult to diagnose irritable bowel syndrome (IBS) because many of its symptoms overlap with other medical conditions. But research has come a long way, and there are several tools doctors can use to diagnose IBS.^1,2

Seeing a gastroenterologist, a doctor who specializes in the stomach and intestines, can help you get a clear diagnosis. They can use diagnostic criteria and certain tests to rule out other conditions like celiac disease and inflammatory bowel disease (IBD).^1,2

Medical history and physical examination

An IBS diagnosis typically begins with a complete medical history and physical exam by your doctor. A medical history may include information about your family history of IBS, any recent infections, medicines you take, and whether you have any stress, depression, or anxiety.^1-3

A physical exam may include looking at your abdominal area for any masses and assessing your body for any current symptoms. The physical exam for diagnosing IBS is used, in part, to rule out other conditions. For example, your doctor will likely ask about any other symptoms like:^1-3

• Fever
• Weight loss
• Hemorrhoids
• Blood in your stool
• Stomach pain that is not linked to a bowel movement

These symptoms may indicate that you have some other medical issue that needs to be addressed.^1-3

Diagnostic criteria for IBS

Once other conditions are ruled out, your doctor may use what is called the Rome criteria for IBS. The Rome criteria helps determine if you have IBS and, if so, what type of IBS you may have.²

The Rome criteria looks at the amount of time you have had IBS symptoms. It states that a person has IBS if they have had stomach pain at least 1 time per week for the past 3 months. That stomach pain also must come along with:²

• A bowel movement
• A change in bowel movements
• A change in frequency of bowel movements

Diagnostic tests

Some tests may be used to ensure a more accurate diagnosis and to rule out other diseases. These tests may include:^1-3

• Stool tests
• Blood tests
• Breath tests
• Other tests

Stool tests

Stool tests analyze your poop. A doctor can use a stool test to rule out such things like bacterial infections or parasite infections. Stool tests can also check for any blood in the stool – which would need further testing – or bile acid, which could be a sign of a problem with the liver.^1-3

Your doctor may ask you to use the Bristol Stool Form Scale to describe the consistency of your poop. Stool consistency helps to define constipation and diarrhea, which helps your doctor determine the best treatment option and monitor your treatment response.⁴

Blood tests

Blood tests for IBS are mostly used to rule out other conditions or look for any “red flag” symptoms. Blood tests can check for low iron in the blood (anemia), celiac disease, and certain infections.^2,3

Breath tests

Two types of breath tests might be used in helping to diagnose IBS. A lactose intolerance breath test can be used to detect whether a person is intolerant to lactose. Lactose intolerance is when the body does not produce enough lactase, an enzyme that helps break down the sugar in dairy products.^1,3

A hydrogen breath test can be used to check for small intestinal bacterial overgrowth (SIBO). SIBO is an increase in bacteria in the small intestine, which can produce gas, bloating, and discomfort. While the symptoms may be similar, it is not the same as IBS.^1,3

Results from these 2 types of breath tests may not conclusively show that a person has IBS. But a doctor can use breath tests to rule out lactose intolerance or small intestinal bacterial overgrowth.^1,3,5

Other tests for IBS

If needed, your doctor may recommend you get additional tests. These are often used to rule out other medical conditions. These tests may include:^1,3,5

• Lower GI series – This is an X-ray used to look at the lower gastrointestinal (GI) tract to see what might be causing digestive symptoms. Someone with IBS would have a normal finding on a lower GI series. This is because IBS does not cause any visible intestinal damage.
• Computed tomography (CT) scan – A CT scan is a type of imaging tool that uses special X-ray equipment to create cross-sectional views of the inside of the body. A CT scan may be used in the diagnosis of IBS, especially if a person has stomach pain.
• Upper endoscopy – An endoscopy is a procedure in which your doctor looks at your throat and esophagus using a thin, flexible tube called an endoscope. Often, they will collect a tissue sample for further testing. This is usually done if they suspect you have celiac disease.
• Colonoscopy – This procedure looks at the inside of the colon and rectum with a flexible tube that is inserted into the anus. A colonoscopy is recommended only if there is evidence of another medical condition that needs to be addressed, such as blood in the stool.