There are no specific tests for IBS, as it does not cause any obvious detectable abnormalities in your digestive system.
In most cases, a diagnosis will be based on whether you have typical symptoms of IBS.
Your GP will consider assessing you for IBS if you have had any of the following symptoms for at least six months:
- abdominal (stomach) pain or discomfort
- a change in bowel habit – such as passing stools more frequently, diarrhoea and/or constipation
A diagnosis of IBS will then be considered if you have stomach pain or discomfort that is either relieved by passing stools, or is associated with a need to go to the toilet frequently or a change in the consistency of your stools.
This should be accompanied by at least two of the following four symptoms:
- a change in how you pass stools – such as needing to strain, feeling a sense of urgency or feeling you have not emptied your bowels properly
- bloating, hardness or tension in your stomach
- your symptoms get worse after eating
- passing mucus from your back passage
Ruling out other conditions
Many cases of IBS can be diagnosed based on your symptoms alone, although sometimes further tests may be needed to check for other possible causes.
For example, your GP may arrange blood tests to rule out other conditions that cause similar symptoms, such as an infection or coeliac disease (a digestive condition where a person has an adverse reaction to gluten).
A sample of your stools will also often be tested for the presence of a substance called calprotectin. This substance is produced by the gut when it is inflamed, and its presence in your stools could mean your symptoms are being caused by inflammatory bowel disease (IBD).
Investigating 'red flags'
Further tests will be needed when you have certain "red flag" symptoms that indicate you may have a potentially more serious condition, such as cancer. These symptoms include:
- unexplained weight loss
- a swelling or lump in your stomach or back passage
- bleeding from your back passage (rectum)
Further testing may also be recommended if you have a family history of bowel cancer or ovarian cancer, or if you are over 60 years of age and have had a change in your bowel habits that has lasted for more than six weeks.
In these cases, your doctor may recommend having a colonoscopy to check for abnormalities in your gut. This is where your rectum and large bowel (colon) are examined using an endoscope, which is inserted into your rectum.