GPAtlas🧭 When to suspect
Irritable bowel syndrome (IBS) is a common, chronic, relapsing–remitting disorder of gut–brain interaction (DGBI): abdominal pain with an altered bowel habit, in the absence of any structural or biochemical abnormality.
The underlying mechanisms are visceral hypersensitivity and disordered motility driven by miscommunication along the gut–brain axis – the bowel is not diseased, it is over-sensitised.
Make a positive diagnosis.
• IBS is recognised on its symptom pattern after a limited, targeted set of tests – it is not a diagnosis of exclusion that justifies open-ended investigation.
• Suspect it when a person has had abdominal pain or discomfort, bloating, or a change in bowel habit for at least 6 months, then confirm against the criteria below.
• Classify by the predominant stool form: IBS-C (constipation), IBS-D (diarrhoea) or IBS-M (mixed).
• IBS is commoner in women and those under 50.
• IBS follows an episode of gastroenteritis in roughly 1 in 10 (post-infectious IBS).
| Step | Criteria |
|---|---|
| Consider IBS | Any of abdominal pain/discomfort, bloating, or a change in bowel habit for at least 6 months. |
| Make a positive diagnosis | • Abdominal pain/discomfort that is either relieved by defecation or associated with altered stool frequency or form, plus at least 2 of: altered stool passage (straining, urgency, incomplete evacuation) • Bloating, distension, tension or hardness • Symptoms worse after eating • Passage of mucus |
| Supporting features | Lethargy, nausea, backache and bladder symptoms are common and support – but do not by themselves make – the diagnosis. |
|
⚠️ Common pitfall • Applying the IBS label too readily in an older patient. • New-onset IBS-type symptoms after the age of 50–60 are uncommon. • The same picture – bloating, altered habit, abdominal pain – is how colorectal and ovarian cancer present. • Never give a first diagnosis of IBS in this group without first excluding malignancy; in women, that means a CA125. |
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