What Is IBS and How Is It Diagnosed?

What is Irritable Bowel Syndrome and how is IBS diagnosed? The four types of IBS and their key symptoms are discussed.

What Is IBS and How Is It Diagnosed? photo

Most people have heard of IBS but you may well ask the question “What is IBS, or irritable bowel syndrome?”

IBS, or irritable bowel syndrome, is a common functional digestive disorder which is characterised by a group of symptoms affecting the gut. Irritable bowel syndrome can also be referred to as spastic bowel, spastic colon, nervous colon, IBS colitis or mucous colitis.

What are the main symptoms of IBS?

Symptoms of IBS can include diarrhoea and/or constipation, bloating, flatulence, abdominal pain and cramps and/or mucus in the stool. Sufferers may have periods of time where they have no symptoms at all followed by periods of flare-ups and can also experience alternating symptoms.

How is IBS diagnosed?

Lots of people say they suffer from IBS but may not have had any investigations or even seen their GP. So how is IBS or irritable bowel syndrome diagnosed?

IBS is diagnosed through investigation and exclusion of other causes using what’s called ‘Rome IV diagnostic criteria’. To do this, your doctor will first look for signs which may indicate another health condition and need further investigation such as anaemia, vomiting, persistent pain, swallowing difficulties, blood in the stool or black and tarry stools, bleeding from your rectum or unexplained weight loss. They may ask questions relating to your family history, what medications you are taking, whether you’ve had any recent infections or life events that may have triggered symptoms, what your diet is like and also ask you about any other associated health conditions that you have.

What is the Rome IV diagnostic criteria?

The Rome IV diagnostic criteria provides medical practitioners with a set of symptom-based criteria which need to be met in order to diagnose IBS. This also helps the practitioner to assess which type of IBS they are dealing with and to choose a treatment which is most likely to be effective in that particular case.

To be eligible for a diagnosis of IBS, the doctor will first check that your symptoms started at least six months ago and that you have experienced recurrent abdominal pain, on average, at least one day per week in the last three months. They will then check whether your pain is associated with two or more of the following:

  • Pain related to your bowel movements – it may get worse or improve after opening your bowels.
  • Pain associated with a change in how often you have a bowel movement.
  • Pain associated with a change in the appearance of your stools.

If you have met these criteria, IBS is then split into four different subtypes (groups) depending on the particular pattern of bowel movements. Treatment recommendations are based on the specific pattern of IBS so it’s important to know which type you have.

What are the four different subtypes of IBS?

IBS-D (diarrhoea-dominant):

  • On days when you have an abnormal bowel movement, more than 25% of your stools are loose or watery and less than 25% of your stools are hard or lumpy

IBS-C (constipation-dominant):

  • On days when you have an abnormal bowel movement, more than 25% of your stools are hard or lumpy and less than 25% of your stools are loose or watery

IBS-M (mixed bowel habit):

  • On days when you have an abnormal bowel movement, more than 25% of your stools are hard or lumpy and more than 25% of your stools are loose or watery

IBS-U (unclassified):

  • Bowel movements do not fall into any of the above subtypes but all other diagnostic criteria for IBS are met.

Camilleri M. (2020). Irritable Bowel Syndrome: Straightening the road from the Rome criteria. Neurogastroenterology and motility : the official journal of the European Gastrointestinal Motility Society, 32(11), e13957. https://doi.org/10.1111/nmo.13957. Available at: https://onlinelibrary.wiley.com/doi/abs/10.1111/nmo.13957