What is IBS, and how is it actually diagnosed?
A disorder of gut-brain interaction producing abdominal pain and altered bowel habit without structural disease — and the diagnostic approach has shifted from excluding everything to positive diagnosis based on symptom pattern, which spares patients years of investigation.
What it actually is. Not a structural abnormality, not inflammation, and not psychological in the dismissive sense. The current understanding involves altered gut motility, visceral hypersensitivity — the gut generating pain signals at normal levels of stretch — changes in the gut microbiome, low-grade immune activation, and altered communication between gut and brain in both directions.
The subtypes, which matter for treatment: predominantly diarrhoea, predominantly constipation, mixed, and unclassified.
How it is diagnosed now. By symptom criteria — recurrent abdominal pain associated with defecation, or with a change in frequency or form of stool — plus a limited set of tests to exclude conditions that mimic it:
Blood tests, including for anaemia and inflammation.
Coeliac serology, since coeliac disease presents very similarly and is frequently missed.
Faecal calprotectin, which distinguishes inflammatory bowel disease from IBS and is the test that has most changed practice.
Further investigation only if red flags are present.
The red flags that change the approach: unintentional weight loss, rectal bleeding, a family history of bowel or ovarian cancer, onset after 50, anaemia, a palpable mass, or nocturnal symptoms waking you from sleep.
What the evidence supports for management:
Dietary approaches, including a low FODMAP diet — which has good evidence and should be done with a dietitian, since it is restrictive, is only a short exclusion phase followed by structured reintroduction, and is frequently done wrongly as a permanent diet.
Soluble fibre, which helps where insoluble fibre worsens symptoms.
Antispasmodics and peppermint oil.
Targeted medication by subtype.
Psychological therapies, including gut-directed hypnotherapy and CBT, which have genuinely good evidence — reflecting the gut-brain axis rather than implying the symptoms are imagined.
Regular meals, exercise and stress management.
General information, not medical advice.