Irritable Bowel Syndrome: When the Diagnosis Is “We Found Nothing”

Dipl. med. Charalampos Romanos, FMH-certified physician · Published: 11 February 2026 · Last medically reviewed: 14 May 2026 · 9 min read

"We investigated everything and found nothing." For many people with irritable bowel syndrome, that is the sentence the workup ends on. It is medically misleading and demoralising for patients. Irritable bowel syndrome is not a fallback diagnosis for when nothing else is left — it is a diagnosis in its own right, with defined criteria. What matters is that the right things were measured beforehand.

IBS is a positive diagnosis

Under the internationally used Rome IV criteria, irritable bowel syndrome is present when recurrent abdominal pain occurs on average at least one day per week over the past three months, associated with at least two of the following: a relationship to defecation, a change in stool frequency, or a change in stool form. Symptoms should date back at least six months.

These are defined criteria — not a label for unexplained abdominal complaints. The distinction matters in practice: a patient who meets the criteria and has no alarm features usually does not need extensive investigation. A patient who does not meet them needs a different explanation.

The alarm features that argue against IBS

Certain findings do not formally exclude irritable bowel syndrome, but they require further investigation before the diagnosis is made:

Unintentional weight loss. Blood in the stool. Anaemia or iron deficiency. First onset after the age of 50. Symptoms that wake the patient at night. Fever. A palpable abdominal mass. A family history of bowel cancer or inflammatory bowel disease. In these constellations, endoscopic assessment is indicated.

What has to be measured before the diagnosis

Even without alarm features there is a baseline workup that should precede the diagnosis — it is narrow, inexpensive and covered by basic insurance:

Full blood count and ferritin. Inflammatory markers. Coeliac serology, because coeliac disease mimics irritable bowel syndrome and is regularly diagnosed late in adults. Faecal calprotectin to distinguish Crohn's disease and ulcerative colitis. TSH, because both over- and underactive thyroid alter bowel habit. These investigations are not optional. They are the reason the diagnosis holds afterwards.

The subtypes — and why they determine treatment

A distinction is made between diarrhoea-predominant (IBS-D), constipation-predominant (IBS-C) and mixed type (IBS-M). This classification is not labelling; it steers treatment. A drug that helps in IBS-D can worsen symptoms in IBS-C. Anyone talking about "IBS" without naming the subtype cannot treat it in a targeted way.

What actually helps

Once the diagnosis is established, there are more effective options than the phrase "there's nothing to be done" would suggest.

Diet. Reducing fermentable carbohydrates — the low-FODMAP approach — improves symptoms in a substantial proportion of patients. How it is done matters: four to six weeks of consistent reduction, then stepwise reintroduction to identify the individual triggers. It is not intended as a permanent diet and impoverishes the gut flora over the long term. Without supervision, a diagnostic instrument turns into an ever-narrower restriction diet.

Medication. Soluble fibre such as psyllium husk is well supported in constipation-predominant disease. Antispasmodics help with cramping pain. Enteric-coated peppermint oil has better evidence behind it than its reputation as a home remedy suggests.

The gut-brain axis. The connection between gut and nervous system is well studied in irritable bowel syndrome. Cognitive behavioural therapy and gut-directed hypnotherapy are among the best-evidenced treatments available. This is not a statement that the symptoms are "psychological" — it is a statement about the physiology of pain processing in the gut.

When treatment does not work

If symptoms persist under consistent standard treatment, extended investigation is justified. Reasonable next steps are then testing for small intestinal bacterial overgrowth (SIBO), particularly with bloating that increases over the day; the question of bile acid malabsorption in treatment-refractory diarrhoea; pancreatic elastase to assess exocrine pancreatic function; and a comprehensive stool analysis.

These investigations belong at the end of the workup, not the beginning. That is exactly the order we work in as part of our Extended Diagnostics.