How IBS is diagnosed in the UK, and the tests to expect

There’s no single test for IBS. A UK GP diagnoses it from what you describe, an examination of your tummy and a short set of tests that look for other causes. Under NICE guideline CG61 those are a full blood count, two markers of inflammation and a coeliac antibody test, and sometimes a poo sample too.

If you were given the label quickly and can’t remember any of that happening, you’re the reader I had in mind. Nothing below tells you whether you have IBS. It tells you what the process is meant to look like, so you can tell whether yours did.

What will the GP ask about?

Expect questions about the symptoms themselves, whether they come and go, how often you get them, when they happen (after certain foods, for example) and how long you’ve had them. The GP may also feel your tummy for lumps or swelling.

Pain sits at the centre of it. The guideline asks clinicians to pin down what the pain or discomfort is like, how much of it there is, where it is and whether that place moves around, because those details help separate IBS from other causes.

You might be shown a chart of poo shapes, the Bristol Stool Form Scale, which saves everyone hunting for polite words. You’ll probably be asked open questions about how this affects your life, such as whether it stops you leaving the house. Answer those fully. About one in five people with faecal incontinence only mention it if they’re asked, and urgency or leaking is part of what a GP needs to hear.

What does a GP look for before calling it IBS?

On paper, IBS is pain or discomfort that eases after opening your bowels, or that comes with a change in how often you go or what your poo looks like. Alongside that, at least two of these:

• a change in passing a stool, such as straining, urgency or feeling you haven’t finished
• bloating, swelling, tension or hardness in the tummy
• symptoms made worse by eating
• passing mucus

Tiredness, nausea, backache and bladder symptoms are common with it too.

Read that as your GP’s checklist, not yours. Plenty of other conditions produce the same things, which is why the tests come first, and why a positive diagnosis is meant to be given only when there are no red flags and the tests find no other cause.

One number in CG61 worries people. It describes assessing people whose symptoms have lasted at least six months. That is a yardstick for the clinician, not a waiting period for you: the NHS advice is to see a GP if you think you might have IBS and have had symptoms for over 4 weeks.

Which tests should I expect?

The first four are the ones CG61 lists for everyone who meets the IBS criteria. Calprotectin was added later, and NICE’s quality standard for IBS names it alongside CRP as a first line test. It’s used when cancer isn’t suspected, and it’s usually part of the picture when your symptoms are mainly diarrhoea or swing between diarrhoea and constipation.

If you’re registered with a GP surgery and aged 16 or over, you can see results that have reached your practice in the NHS App or your NHS account. That’s the quickest way to find out which tests were done, if you’ve lost track.

Which tests won’t I usually need?

For someone who meets the IBS criteria, the guideline says these are not necessary to confirm it:

• ultrasound
• rigid or flexible sigmoidoscopy
• colonoscopy or barium enema
• thyroid function tests
• a stool test for ova and parasites
• faecal occult blood
• the hydrogen breath test, for lactose intolerance and bacterial overgrowth

Not necessary to confirm IBS isn’t the same as never. A GP may arrange one of these for a different reason, such as a FIT kit, a home poo test that checks for bleeding from the bowel, when bowel cancer needs to be ruled out. Hospital tests aren’t usually needed unless the GP isn’t sure what the problem is. If someone has offered you a private breath test instead, I’ve written about that separately in should I get a SIBO test.

Why does the coeliac test matter so much?

Because coeliac disease shares many of its gut symptoms with IBS, and the test is easy to spoil. IBS in adults is on the NHS list of reasons to be tested.

The blood test looks for antibodies your body makes in response to gluten, so you need gluten in your diet when it’s done. Avoiding it could lead to an inaccurate result. Don’t start a gluten free diet until a specialist confirms the diagnosis, even if the blood test is positive. If you’ve already cut gluten out, tell the GP before the blood is taken. There’s more on this in does bread make you bloated.

When does a GP refer to hospital instead?

When there are red flags. CG61 asks clinicians to examine everyone with possible IBS for warning signs, meaning signs and symptoms of cancer as set out in NICE’s suspected cancer guideline and inflammatory markers that point to inflammatory bowel disease, and to refer to a hospital specialist if any are present.

You don’t need to work out where you sit in that. You need to know which symptoms mean you don’t wait for a routine appointment. These are the NHS’s own words.

Ask for an urgent GP appointment or get help from NHS 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”

Call 999 or go to A&E if: “a stomach ache came on very suddenly or is severe”, “it hurts when you touch your stomach”, “you’re vomiting blood or your vomit looks like ground coffee”, “your poo is bloody or black and sticky and extremely smelly”, or “you cannot poo or fart”.

What happens once it’s called IBS?

The GP should talk you through what IBS is and what the options are. It’s a lot to take in at once, and if you leave unsure about something, writing your questions down and booking another appointment to go over them is the expected next step, not a nuisance.

After that, follow up is meant to be agreed between you. NICE’s IBS quality standard says adults with IBS agree how often they’ll review it and whether by phone or face to face, and should be encouraged to make contact to arrange it. If a warning sign turns up later, that prompts further investigation or a referral, whatever the label says.

If you feel the label arrived before the checks did, when your GP says it’s IBS and you don’t feel heard has the words to use. If bloating is the symptom that brought you here and you’re not sure what to do next, the six questions in the bloating quiz end with a next step, not a diagnosis.