IBS must always been diagnosed by a physician. IBS is at present diagnosed after excluding structural or biochemical abnormalities.

The physician will consider the differential possibilities from the signs and symptoms in order to reach a positive or negative diagnosis for IBS.

The cornerstone of the diagnosis is a detailed history and a thorough physical examination. Laboratory investigations of blood and stools, x-rays and endoscopic procedures are often useful to rule out organic disease.

This is necessary because the main worry of patients (and doctors) is often serious pathology such as inflammatory bowel disease or (colon) cancer.

In fact, for patients under the age of 40, IBS can usually be diagnosed by relevant symptoms revealed during history taking and the lack of abnormal signs on physical examination. Other investigations might of course be needed, each case being judged on its merits by the physician.

The physician who suspects IBS will often use the so called Manning criteria:

In 1978 the Manning criteria of IBS were published and they are used all over the world to diagnose IBS:

If the first four symptoms are present, it is highly likely that the patient suffers from IBS. The last two symptoms also often occur in IBS patients, but are not as distinctive for IBS as the first four.

The manning criteria

1. visible abdominal distension
2. relief of pain with/after bowel movement
3. more frequent bowel movements with the onset of pain
4. loose stools at onset of pain
5. passage of mucus via the rectum
6. feeling of incomplete evacuation

In 1988 an international consensus meeting was held by gastroenterologists in Rome and they further specified the criteria for IBS. These criteria were revised in 1999 and they now form the standard for the IBS diagnosis:

The Rome II criteria for IBS (Irritable Bowel Syndrome)

At least twelve weeks or more, which need not be consecutive, in the preceding 12 months, of abdominal discomfort or pain, that has two out of the three features:

1. relieved with defecation and/or
2. onset associated with a change in frequency of stool and/or
3. onset associated with a change in form(appearance)of stool

Symptoms that cumulatively support the diagnosis of Irritable Bowel Syndrome:

• abnormal stool frequency (> 3/day or <3/week)
• *abnormal stool form (lumpy/hard or loose/watery)
• abnormal stool passage (straining, urgency, or feeling of incomplete evacuation)
• passage of mucus
• bloating or feeling of abdominal distension

*Bristol stool form scale (BSF-Scale) is a diagnostic aid to classify the stool form into 7 groups. Because the form of the stool depends on the time it spends in the colon, there is a correlation between the colonic transit time and the BSF type.