Rome V retired the word functional

There is no blood test for irritable bowel syndrome. What exists instead is a definition: a list of symptoms, at a stated frequency, over a stated period, agreed by a committee and revised every decade or so. Those are the Rome criteria, and researchers use them to decide who enters a trial while clinicians use them to name what someone has.

The fifth revision landed in May 2026, in the journal Gastroenterology, ten years after the fourth. Its opening sentence does something a diagnostic manual rarely does — it drops a word. Bowel disorders, it says, were previously termed functional bowel disorders.

Six categories, one fewer adjective

The revision sorts these conditions into six: irritable bowel syndrome, chronic constipation, functional diarrhoea, functional abdominal bloating, unclassified bowel disorder, and opioid-induced constipation. Each is defined and then worked through in the same order — how common it is, why the criteria changed, how it is assessed, what is understood about the mechanism, and how it is treated. The stated reason for revising at all is that ten years of research changed what was known about all five of those things.

The word that went is worth a moment. Functional had come to mark the leftover category: the diagnosis you were given when the tests came back normal and there was nothing else to call it. The field now describes these as disorders of gut–brain interaction — chronic symptoms with no structural or biochemical cause that routine investigation can find, which is a statement about what the tests can see, not about whether something is happening.

Why this matters more if you have IBD

Traditional practice held that irritable bowel syndrome should only be diagnosed in someone with no organic disease that could explain the symptoms — which, read strictly, means it can never be diagnosed in inflammatory bowel disease. The view gaining ground in neurogastroenterology is different: symptoms may be out of proportion to the disease activity that can be seen, so the visible inflammation is simply not enough to explain what someone feels.

That is why the same review argues for a positive diagnosis rather than a diagnosis of exclusion — one made on the pattern of symptoms rather than on the absence of everything else. Its stated reasons are practical: naming the thing validates the experience, reduces anxiety, and allows treatment to start earlier and aim at something. Its stated caution is equally practical, and it is the subject of the previous post: in inflammatory bowel disease there really are other conditions that mimic this one, and they have to be looked for.

What criteria are for, and what they are not

Within weeks of the new criteria appearing, a team in Leeds tested them against the previous two. Among 726 people referred to a specialist clinic with suspected irritable bowel syndrome, 417 — 57 percent — met the new definition. Measured against the study’s reference standard, sensitivity was 66.1 percent and specificity 80.1 percent, where the 2016 criteria had scored 78.9 and 81.0 percent, and the 2006 criteria 87.5 and 75.0 percent. Agreement between the old and new definitions was only fair to moderate.

The authors’ own conclusion is that the new criteria identify a different group of people, with lower sensitivity than either predecessor, and that the clinical relevance of this is uncertain. That study was done in people referred with suspected irritable bowel syndrome, not in people with inflammatory bowel disease, so it says nothing directly about the overlap.