A proper medical history is usually sufficient to diagnose irritable bowel syndrome (IBS) in patients and there are no specific tests to diagnose it. However, the physician may ask for certain tests to rule out other conditions that may mimic irritable bowel syndrome (IBS). Some of the investigations that may be performed for this purpose include:

Blood tests

Stool test

Sigmoidoscopy or colonoscopy

Computerized tomography scan (CT scan) of abdomen and pelvis

Lactose intolerance tests - Tests may be done to find out if you have intolerance to lactose (which is found in milk and milk products)

If the results of these tests do not substantiate diagnosis of any other disease condition, the physician may confirm the diagnosis of irritable bowel syndrome (IBS).

Rome criteria for diagnosing irritable bowel syndrome (IBS):

According to Rome criteria for IBS, a patient must have the following symptoms for at least 12 weeks in the previous 12 months; these weeks need not be consecutive:

Abdominal pain which is:

Relieved by passage of stools

Accompanied by change in frequency of stools at the onset

Accompanied by change in consistency of stools at the onset

In addition, the patient must also have two of the following features at least 25% of the times:

Altered stool frequency

Altered stool form

Altered passage of stools (straining, urgency, etc.)

Mucus with stools

Bloating of abdomen

These criteria are often used by physicians in the clinic set-up to diagnose irritable bowel syndrome (IBS).