Author: Dr Henry Wei. Sources checked 18 October 2026.
A practical IBS consultation
Assess
Identify the bowel pattern and alarm features, then review previous treatment and its actual response.
Assess
Identify the bowel pattern and alarm features, then review previous treatment and its actual response.
Investigate
Use FBC, CRP and coeliac serology initially. Add calprotectin, FIT, infection testing or colonoscopy according to the clinical question.
Explain and begin treatment
Describe IBS as a disorder of gut–brain interaction, including altered sensitivity and motility. Begin treatment with a clear goal.
Target therapy and review
Match treatment to the dominant symptoms and adequate previous trials. Review the response and adjust or stop ineffective treatment.
Read all four steps
Assess
Identify the bowel pattern and alarm features, then review previous treatment and its actual response.
Investigate
Use FBC, CRP and coeliac serology initially. Add calprotectin, FIT, infection testing or colonoscopy according to the clinical question.
Explain and begin treatment
Describe IBS as a disorder of gut–brain interaction, including altered sensitivity and motility. Begin treatment with a clear goal.
Target therapy and review
Match treatment to the dominant symptoms and adequate previous trials. Review the response and adjust or stop ineffective treatment.
1. Assess the pattern and previous treatment
Assess recurrent abdominal pain or discomfort and its associations with defaecation, stool frequency and stool form. Identify constipation, diarrhoea or a mixed pattern, and ask which symptom most affects daily life.
Check for bleeding, iron deficiency anaemia, weight loss, a mass, nocturnal diarrhoea and relevant family history. IBS can present at any age, but new symptoms later in life need an age-appropriate assessment.
Review what has already been tried: the dose, duration, adherence, benefit and side effects. A brief or poorly tolerated trial may need a different approach.
Rome V symptom criteria
Recurrent, non-continuous pain or discomfort on at least three days a month over the last three months, with onset at least six months earlier, and at least two associations: defaecation, altered stool frequency or altered stool form.
2. Investigate appropriately
Start with FBC, CRP and coeliac serology, while the patient is eating gluten.
- Diarrhoea: consider faecal calprotectin for possible IBD, and stool infection tests when the history suggests infection.
- Possible colorectal cancer: consider FIT within the symptomatic assessment pathway. A negative result does not replace an otherwise indicated colonoscopy.
- Colonoscopy may be appropriate for alarm features, abnormal results, concerning new symptoms or persistent watery diarrhoea. Request colonic biopsies when microscopic colitis is suspected, even if the lining looks normal.
3. Explain the diagnosis and begin treatment
When the symptom pattern and assessment support IBS, give a clear diagnosis and explain what the investigations have checked. Treatment can usually begin after a limited assessment.
IBS is a disorder of gut–brain interaction. Visceral hypersensitivity, altered motility and the processing of gut signals contribute to pain and bowel changes. Food fermentation, post-infectious changes and stress can influence symptoms. A normal endoscopy does not assess these mechanisms.
Start with regular meals, activity and gradual soluble fibre where appropriate. Agree the first treatment and a realistic goal, such as less urgency at work or more comfortable bowel movements.
4. Target treatment and review the response
Choose treatment from the dominant symptom and previous response. Make one change at a time where practical.
| Main symptom | Options | Clinical pearl |
|---|---|---|
| Constipation | Gradual psyllium; add or adjust macrogol. | Persistent straining despite soft stool may need assessment for an evacuation disorder. |
| Diarrhoea or urgency | Loperamide, adjusted to stool consistency and urgency. | Bowel control may improve without relieving pain. Persistent watery diarrhoea warrants review for other causes. |
| Pain or cramping | Mebeverine or peppermint oil; consider low-dose amitriptyline for persistent pain. | Peppermint may worsen reflux. Amitriptyline is off-label for IBS and may cause sedation or constipation. |
| Bloating or food-related symptoms | Review portions and triggers; consider a dietitian-led low-FODMAP trial. | Reintroduce foods after restriction. More bran can worsen bloating. |
| Persistent symptoms affecting daily life | Consider gut-directed CBT or hypnotherapy alongside other treatment. | These therapies target gut sensitivity and symptom responses. |
Other options and persistent symptoms
A time-limited probiotic trial is optional; benefits vary between products. Evidence for acupuncture is less certain. Consider bile acid diarrhoea or selected SIBO assessment when the history supports them.
Agree a review date. Check symptom relief, daily function and adverse effects, and stop ineffective treatment. Refer for diagnostic uncertainty, nutritional restriction or disabling symptoms despite adequate trials.
Clinical pearls
- Bloating alone does not establish IBS.
- Check the treatment dose and duration before calling it ineffective.
- Food-IgG and commercial microbiome panels do not diagnose IBS. Discuss the evidence when patients ask about them.
Information to share with your patient
Related clinician articles
References
- Rome Foundation: Rome V bowel-disorder criteria, 2026
- bpacnz: dietary management of IBS, Best Practice Bulletin 118
- Health NZ: irritable bowel syndrome
- BSG: guideline on the management of IBS, 2021
- Monash University: the three-step FODMAP diet
- ATLANTIS: amitriptyline for IBS in primary care, Lancet 2023
- Medsafe: Amirol data sheet
- Medsafe: Colofac data sheet
- Health NZ: lower-bowel investigations for patients with symptoms
- NIDDK: IBS symptoms and mechanisms