Updated 16 August 2018

Diagnosing IBS

There are no tests to diagnose IBS, but here are certain criteria that need to be met before a diagnosis of IBS can be made.

The correct diagnosis and appropriate treatment for irritable bowel syndrome (IBS) is challenging. There are no specific tests (biochemical or pathological) that can assist in making the diagnosis.

Therefore, doctors rely heavily on the patient’s description of their symptoms to make a diagnosis.

The diagnosis is often made by exclusion, especially by less experienced doctors, which means that a lot of expensive tests are requested, but that all come back with normal results. 

Over the years, several symptom criterions have been developed to assist doctors in their diagnosis of IBS. This moved from the Manning criteria and Kruis scoring system to the Rome I, Rome II, Rome III and now Rome IV criteria for a symptom-based diagnosis. 

The Rome IV criteria are as follows:

Recurrent abdominal pain, on average, at least one day per week in the last 3 months, associated with two or more of the following criteria:

  • Related to defecation.
  • Associated with a change in frequency of stool.
  • Associated with a change in form (appearance) of stool.

Symptoms must have started at least 6 months ago.

For all criteria, the following hold: no evidence of an inflammatory, anatomic, metabolic, neoplastic or biochemical process that explains symptoms. 

Differential diagnosis

Before IBS is diagnosed, other gut-related diseases need to be ruled out. These include: 

  • Inflammatory bowel disease (IBD, which includes ulcerative colitis and Crohn’s disease)
  • Gastro-oesophageal reflux disease (GORD)
  • Food intolerances (e.g. lactose intolerance, fructose intolerance)
  • Food allergies (e.g. Coeliac disease, wheat allergy) 
  • Neurological issues 


Irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) have symptoms that overlap with one another, but they’re not the same condition. IBD produces positive results when pathology and biochemical tests are ordered, whereas people with IBS show no sign of disease or abnormalities when the colon is examined or when biochemical tests are ordered.

The two conditions involve very different treatments. Therefore, getting an accurate diagnosis is essential to managing your condition properly.


Gastro-oesophageal reflux disease (GORD) is also very different to the heartburn that people with IBS may experience. Heartburn associated with IBS is far less severe than the heartburn experienced by people with GORD. GORD is a chronic digestive disease that occurs when stomach acid or stomach contents flow back up into the oesophagus.

The backwash (reflux) irritates the lining of the oesophagus and can damage it. Prolonged damage may place the affected person at high risk for oesophageal cancer. 

IBS vs. food intolerances

Lactose and fructose intolerances can be diagnosed via a positive hydrogen breath test. People with IBS may not be able to digest lactose and fructose well, but differ from people who have been diagnosed with lactose or fructose intolerance. The symptoms of people with intolerances improve once they make the necessary dietary changes.

IBS vs. food allergies 

Food allergies can be diagnosed using skin prick tests or a radioallergosorbent (RAST) blood test. People with IBS would have normal test results if they were to undergo either of these. This indicates that pathology isn’t present. Individuals with food allergies will start to feel better once the necessary dietary changes have been made. 

IBS vs. neurological disorders

Neurological disorders such as autonomic neuropathy can be the cause of constipation. Autonomic neuropathy involves damage to the nerves that carry information from the brain and spinal cord to the intestines, thus affecting digestion. This disorder is often diagnosed in conjunction with other medical issues such as diabetes.

It’s also sometimes linked to cancer treatment. Various tests are available to diagnose neurological disorders. 

Read more:
Treating IBS

Reviewed by Kim Hofmann, registered dietitian, BSc Medical (Honours) Nutrition and Dietetics, BSc (Honours) Psychology. January 2018.


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.