What IBS is, and how a doctor decides

Written by Kathryn Dunn · Published 23 October 2026 · Last reviewed 23 October 2026

You've had the tests. Blood, maybe a stool sample, maybe more. They came back clear. Then somebody said Irritable Bowel Syndrome, or IBS, and the relief that nothing serious was wrong lasted about a day. After that you noticed you still had the same stomach and no plan.

This page is what the diagnosis means, how a doctor is supposed to get to it, and the symptoms that aren't IBS and need a doctor now.

What IBS is

IBS is a long-term condition of the gut. The gut and the brain are communicating in an over-sensitive way, and the result is pain or discomfort in the abdomen linked to your bowels, together with a change in how often you go or what it's like when you do ^[1]. The NHS lists the main symptoms as stomach pain or cramps, usually worse after eating and better after going; bloating; diarrhoea; and constipation ^[2].

It's common, it's real, and it isn't dangerous. It also isn't the same as having a sensitive stomach, and it isn't something you've brought on yourself. There's a whole page on this site about why the gut and the brain behave this way.

Doctors sort IBS into four patterns, depending on what your bowels mostly do: mainly constipation, mainly diarrhoea, a mix of both, or neither clearly. Which one you are matters a little for which treatment gets tried first, and there's a short page on that.

How common it is

Depends who's counting, and on which definition they use. Guts UK puts it at somewhere between four and ten people in every hundred ^[3]. The largest pooled survey of symptoms found about one in eleven people met the older diagnostic criteria and about one in twenty-six met the stricter current ones ^[4]. Part of that gap is definition. Part of it is the people managing it without ever having been told what it is. Women are more likely to have it than men, by about half as much again ^[5], and are diagnosed about twice as often ^[3].

How a doctor decides it's IBS

There's no test for IBS. That surprises people, and it's the thing to understand about how the diagnosis works. It's made on the pattern of your symptoms, plus a short set of tests whose job is to rule other things out ^[2][6].

Here's what the NHS and NICE say should happen ^[2][6]. Your GP asks about the symptoms: what they are, how long you've had them, whether they come and go, and what sets them off. NICE expects the symptoms to have been going on for at least six months before IBS is considered. They may feel your abdomen for lumps or swelling. Then they run the tests. A blood test, which checks for anaemia and inflammation and for coeliac disease. Usually a stool sample, which checks for infection and for inflammation of the kind seen in inflammatory bowel disease ^[7].

That's normally it. If those come back clear and your symptoms fit the pattern, it's IBS. You won't usually need a camera test or a hospital referral unless something in the history or the tests says otherwise ^[2]. NICE lists a set of tests that are not needed to confirm IBS, including ultrasound, endoscopy and breath tests ^[6]. If you were sent for several of those, it was for a reason, and it's fair to ask what it was.

If you weren't asked about the symptoms above, or the blood and stool tests weren't done, that's worth going back about. The diagnosis is only as good as the ruling-out that went into it.

The criteria, in plain English

Doctors measure the symptom pattern against a set of international criteria written by the Rome Foundation. They changed in 2026 ^[1].

Under the new criteria, discomfort counts again, not only pain. The threshold is pain or discomfort on at least three days a month over the last three months, down from the old rule of at least one day a week. And continuous pain has been separated out, because pain that never lets up points to something other than IBS ^[1].

If you were told some years ago that your symptoms were too mild or too infrequent to count as IBS, they may count now. There's a longer page on the new rules and who they include.

The symptoms that aren't IBS

Read this section even if you've had IBS for years. These are the NHS's own words ^[2]. Ask for an urgent GP appointment, or call 111, if:

• you have lost a lot of weight for no reason
• you're bleeding from your bottom or have bloody diarrhoea
• you find a hard lump or swelling in your tummy
• you have shortness of breath, noticeable heartbeats (palpitations) and skin that's paler than usual

NICE tells GPs to check for the warning signs in its separate guideline on suspected cancer, which is where the age-based rules live, and to look for the inflammation markers that point to inflammatory bowel disease ^[6][8]. Pain or diarrhoea that wakes you at night is worth saying out loud too: the specialists' guideline treats it as atypical for IBS and a reason to look further ^[9].

None of these means you've got something serious. All of them mean IBS shouldn't be assumed until a doctor has checked. Say the words, don't wait, and don't talk yourself out of it because you've had IBS before.

What IBS isn't

A few conditions get mistaken for it, which is what the tests are for.

Coeliac disease, where gluten damages the gut; the blood test checks for it. Inflammatory bowel disease, meaning Crohn's disease and ulcerative colitis; the stool test for inflammation helps separate them from IBS ^[7]. Bile acid diarrhoea, which can look exactly like IBS with diarrhoea, is more common than most people think and treatable once found; the BSG guideline says testing for it should be considered, especially when the diarrhoea is severe or happens at night ^[9], and there's a page coming on it. And in women, endometriosis and, rarely, ovarian cancer can present with bloating and bowel changes, which is why the family history question matters ^[6].

"It's just IBS"

If you were handed the diagnosis and sent home, you've had the first half of the process. IBS is a real diagnosis of a real condition, and it has a treatment pathway behind it, in writing, in the guidelines your GP follows. Being told what it is was the start. The next page is about what to do when the sentence ends there.