How is IBS diagnosed?

IBS is diagnosed clinically using the Rome IV criteria — recurrent abdominal pain at least once per week for the past 3 months, associated with changes in stool frequency or form, or relieved or worsened by defecation. There is no single diagnostic test for IBS. Tests (blood count, CRP, coeliac antibodies, faecal calprotectin) are done to exclude other conditions. A normal faecal calprotectin result strongly supports IBS over inflammatory bowel disease.

What is the difference between IBS and IBD?

IBS (Irritable Bowel Syndrome) is a functional disorder — bowel function is altered (pain, bloating, diarrhoea, constipation) but the gut lining appears structurally normal on investigation. IBD (Inflammatory Bowel Disease — Crohn's disease and ulcerative colitis) involves actual inflammation and damage to the gut wall, confirmed on colonoscopy and biopsy. Key distinguishing features: IBD often causes rectal bleeding, nocturnal symptoms, weight loss, and elevated inflammatory markers (CRP, faecal calprotectin). IBS does not.

Diet does not cause IBS, but certain foods consistently trigger symptoms. FODMAPs (fermentable carbohydrates) are the most evidence-based dietary trigger — they draw water into the bowel and ferment rapidly, causing bloating and altered motility in people with IBS. Other common triggers include caffeine, alcohol, fatty foods, and large meals. The low-FODMAP diet — developed at Monash University — is the most evidence-based dietary intervention, reducing symptoms in 50–75% of patients.

Is IBS a lifelong condition?

IBS is a chronic condition but its severity fluctuates. Many patients have periods of minimal or no symptoms, particularly with effective management (dietary modification, stress management, medication when needed). A significant proportion of patients experience symptom improvement over time, and some achieve long-term remission. IBS does not progress to IBD or colorectal cancer — it is not a precancerous condition.

What medications are used for IBS?

Medication is symptom-directed. For IBS-D (diarrhoea-predominant): loperamide (Imodium) for acute episodes; antispasmodics (hyoscine, mebeverine) for pain and cramps; low-dose tricyclic antidepressants (amitriptyline) for pain modulation. For IBS-C (constipation-predominant): osmotic laxatives (polyethylene glycol), linaclotide, or lubiprostone. Peppermint oil capsules have evidence for abdominal pain and bloating. Gut-directed psychotherapy (CBT, hypnotherapy) has equivalent evidence to pharmacotherapy for overall symptom reduction.

Preparing for Appointments with IBS

Quick answer: Keep a detailed food and symptom diary for at least 2 weeks before your appointment — recording everything you eat, your bowel habit (frequency, consistency using the Bristol Stool Form Scale), and pain or bloating episodes with their timing relative to meals. IBS is a clinical diagnosis based on symptom patterns (the Rome IV criteria); objective diary data is the most useful information you can bring.

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal conditions worldwide, affecting 10–15% of the population. It is a functional diagnosis — meaning tests are normal, and the condition is defined by symptom patterns rather than structural findings. This makes the quality of your symptom history the single most important input at the appointment.

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The Rome IV Criteria — What Your Doctor Is Assessing

IBS is diagnosed using the Rome IV criteria. Your doctor is looking for:

Recurrent abdominal pain — on average at least 1 day per week in the last 3 months
Associated with 2 or more of:
- Related to defecation (pain improves or worsens with a bowel movement)
- Associated with a change in stool frequency
- Associated with a change in stool form (appearance)
Symptoms present for the last 3 months, with onset at least 6 months before diagnosis

IBS is further classified by predominant bowel habit: IBS-C (constipation-predominant), IBS-D (diarrhoea-predominant), IBS-M (mixed), or IBS-U (unclassified).

What to Track Before Your Appointment (2 Weeks)

Every meal and drink: What, when, and approximately how much. Include snacks, coffee, alcohol, and any supplements. A Doctor Appointment Journal or food diary app makes this consistent and easy to hand over.
Bowel habits: Number of movements per day, urgency, straining, sense of incomplete emptying
Stool consistency: Use the Bristol Stool Form Scale — Types 1–2 (hard, lumpy) indicate constipation; Types 6–7 (liquid, watery) indicate diarrhoea; Type 4 (smooth sausage) is ideal
Pain/bloating: Location, severity (0–10), timing (before, during, or after eating), what relieves it
Stress and sleep: IBS symptoms frequently worsen with stress — note major stressors and sleep quality
Menstrual cycle (if applicable): IBS symptoms often worsen perimenstrually

Warning Symptoms — Report These First

The following are red-flag symptoms that require urgent investigation to exclude inflammatory bowel disease, coeliac disease, or colorectal cancer — they are NOT consistent with uncomplicated IBS:

Blood in stool (rectal bleeding)
Unexplained weight loss
Nocturnal symptoms waking you from sleep
Progressive difficulty swallowing
Family history of colorectal cancer or IBD (Crohn’s disease, ulcerative colitis)
Symptom onset after age 50
Anaemia (iron deficiency)
Fever with GI symptoms

What Investigations to Expect

IBS is a clinical diagnosis of exclusion. Tests are done to rule out other conditions, not to confirm IBS:

Blood tests: Full blood count (anaemia), CRP/ESR (inflammation), coeliac antibodies (tTG-IgA — coeliac disease mimics IBS-D), thyroid function (hypothyroidism causes constipation)
Stool tests: Faecal calprotectin (distinguishes IBS from inflammatory bowel disease — elevated in IBD, normal in IBS); stool culture if infective diarrhoea suspected
Colonoscopy: Not routinely needed for typical IBS presentation in younger patients. Indicated for red-flag symptoms, age over 50, or abnormal blood/stool tests.
Breath tests: Hydrogen breath test for small intestinal bacterial overgrowth (SIBO) or lactose/fructose intolerance — ordered when bloating and diarrhoea predominate

Questions to Ask

Based on my symptoms, which IBS subtype do I have — and does that change the treatment approach?
Should I try a low-FODMAP diet, and do you have a referral to a dietitian who specialises in this?
Are there medications appropriate for my predominant symptoms — antispasmodics, loperamide, or laxatives?
Should I be tested for SIBO or food intolerances?
Is there a role for gut-directed psychotherapy (CBT or hypnotherapy) for my symptoms?

The Low-FODMAP Diet — What It Is

FODMAPs are fermentable carbohydrates (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols) that draw water into the bowel and are fermented by gut bacteria, causing gas, bloating, and altered bowel habit in IBS patients. The low-FODMAP diet is a structured 3-phase elimination and reintroduction protocol — it is not a permanent elimination diet. It should be done under dietitian supervision. Evidence shows it reduces symptoms in 50–75% of IBS patients.

High-FODMAP foods to limit initially: wheat, rye, onion, garlic, apples, pears, stone fruits, legumes, lactose-containing dairy, and artificial sweeteners (sorbitol, mannitol, xylitol).

Regional Notes

Singapore: IBS managed by GPs and gastroenterologists at restructured hospitals and private GI clinics. Dietitian referral for low-FODMAP available at SGH Nutrition and Dietetics. Faecal calprotectin testing available at major labs (SGD 60–120). Colonoscopy: SGD 1,000–2,500 subsidised; private SGD 2,500–4,500.

Australia: GP-managed initially; gastroenterology referral for red flags or treatment-refractory cases. Dietitian services rebatable under CDM plan (up to 5 sessions). Monash University (Melbourne) is the global authority on the low-FODMAP diet — free app available for food checking.

United States: Managed by primary care or gastroenterologist. Low-FODMAP dietitians available in major centres. American College of Gastroenterology IBS guidelines published 2021 — available online for patient reference. Faecal calprotectin covered by most insurers with appropriate indication.

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Medical Disclaimer: This guide is for informational and preparation purposes only. It does not constitute medical advice, diagnosis, or treatment. Always consult a qualified medical professional for guidance specific to your situation.