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Diagnosis n treatment of IBS.

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Quick answer

Diagnosis of irritable bowel syndrome (IBS)

IBS is a disorder of gut-brain interaction: recurrent abdominal pain with altered bowel habits, without structural disease explaining it.

Rome IV clinical criteria

Diagnose IBS when there is recurrent abdominal pain, on average, at least 1 day per week in the last 3 months, associated with at least 2 of:
  1. Related to defecation
  2. Change in stool frequency
  3. Change in stool form or appearance
Symptoms should have begun at least 6 months before diagnosis.

Subtypes

Use stool pattern on days with abnormal bowel movements:
  • IBS-C: constipation-predominant
  • IBS-D: diarrhea-predominant
  • IBS-M: mixed constipation and diarrhea
  • IBS-U: unclassified

Initial assessment

History, examination, medication/diet review, and limited testing are usually sufficient if symptoms fit IBS and there are no warning features. Common initial tests include:
  • CBC
  • CRP or fecal calprotectin if diarrhea is prominent, to help exclude inflammatory bowel disease
  • Coeliac serology in IBS-D or IBS-M
  • Stool testing only if infection risk is suggested

Red flags: investigate or refer

IBS should not be assumed if there is:
  • Rectal bleeding or black stools
  • Unintentional weight loss
  • Iron-deficiency anemia
  • Fever, nocturnal diarrhea, persistent vomiting
  • New symptoms at older age
  • Family history of colorectal cancer, inflammatory bowel disease, or coeliac disease
  • Palpable abdominal/rectal mass
These may require colonoscopy, imaging, or specialist assessment.

Treatment of IBS

Treatment is individualized according to the predominant bowel pattern and most troublesome symptoms.

1. General measures for all patients

  • Explain the diagnosis and reassure: IBS is real and can be managed, but often fluctuates.
  • Regular meals, adequate sleep, physical activity, stress management.
  • Keep a symptom-food-stool diary.
  • Avoid obvious individual triggers, but do not impose unnecessarily restrictive diets.
  • Consider soluble fiber such as psyllium/ispaghula. Increase gradually with water.
    • Avoid or limit insoluble bran if it worsens bloating or pain.

2. Dietary treatment

  • A short, supervised low-FODMAP diet can improve bloating, pain, and bowel symptoms. It has three phases: restriction, food reintroduction, then personalization. Ideally work with a dietitian.
  • In IBS-D, reduce alcohol, caffeine, fatty foods, and sugar alcohols if these trigger diarrhea.
  • A trial of lactose restriction can be reasonable only if lactose intolerance is suspected.
  • Gluten avoidance is not routinely needed unless coeliac disease is present or a clear individual response occurs.

3. Pain and bloating

  • Peppermint oil, enteric-coated, may help cramping and bloating. Avoid if it causes reflux.
  • Antispasmodics such as hyoscine butylbromide, dicyclomine, or mebeverine may help episodic cramps. Anticholinergic adverse effects can include dry mouth, blurred vision, and constipation.
  • For persistent pain, low-dose tricyclic antidepressants such as amitriptyline are often useful, especially in IBS-D. They are used for neuromodulation, not because symptoms are “all psychological.”
  • SSRIs may be considered when anxiety/depression is prominent, especially if constipation predominates, though pain evidence is less consistent.
Avoid opioids, which can worsen bowel function and cause dependence.

4. IBS with constipation (IBS-C)

Stepwise options:
  • Soluble fiber, particularly psyllium
  • Polyethylene glycol (PEG/macrogol) for constipation, though it may not improve pain
  • Secretagogues where available: linaclotide, lubiprostone, plecanatide, tenapanor
  • Consider pelvic-floor assessment/biofeedback if defecatory dysfunction is suspected

5. IBS with diarrhea (IBS-D)

Options:
  • Loperamide for diarrhea/urgency. It improves stool frequency and consistency but is less effective for pain or bloating.
  • Consider a trial of a bile-acid sequestrant if bile-acid diarrhea is suspected.
  • Rifaximin may help selected patients with persistent IBS-D, depending on local availability and clinician guidance.
  • Eluxadoline is an option in some settings, but must not be used in people without a gallbladder, with biliary obstruction, pancreatitis risk, substantial alcohol use, or severe liver disease.
  • Low-dose tricyclic antidepressant can help pain plus diarrhea.

6. Psychological and behavioral therapies

For ongoing symptoms, especially where stress or symptom-related anxiety is significant:
  • Gut-directed cognitive behavioral therapy
  • Gut-directed hypnotherapy
  • Mindfulness or relaxation-based therapy
These therapies can reduce symptom severity and improve quality of life.

Practical first-line plan

  1. Confirm no red flags and perform appropriate limited screening tests.
  2. Identify subtype: IBS-C, IBS-D, or IBS-M.
  3. Start soluble fiber and regular lifestyle measures.
  4. Trial targeted dietary change, often low-FODMAP with guided reintroduction.
  5. Add symptom-directed medicine: antispasmodic/peppermint for pain, PEG or IBS-C drug for constipation, loperamide for diarrhea.
  6. If symptoms persist, consider a gastroenterologist, dietitian, and gut-brain therapy.
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