Should I get a SIBO test? What UK guidance says

Not if your symptoms look like typical IBS, according to UK guidance. NICE lists the hydrogen breath test for bacterial overgrowth among tests that aren’t necessary to diagnose IBS, and the British Society of Gastroenterology’s 2021 guideline says there’s no role for it in typical IBS. SIBO itself is real, and mostly follows surgery or another condition.

This page explains the guidance. It isn’t a ruling on your own case, which is a conversation for your GP or a gastroenterologist.

What is SIBO?

SIBO stands for small intestinal bacterial overgrowth: more bacteria living in the small bowel than should be there. Most of your gut bacteria live further down, in the large bowel. When surgery or a disease changes the structure of the small bowel, or how quickly things move through it, bacteria can build up where they don’t belong, and that can affect how well food is absorbed.

The symptoms are vague and shared with plenty of other gut problems: tummy pain, bloating, diarrhoea, pale or greasy poo, weight loss, and low levels of vitamins or minerals such as iron, vitamin B12 or calcium. That overlap is a big part of why the testing question gets so heated.

Who is SIBO more likely in?

People whose gut has been changed by surgery or by a diagnosed condition. On the list are operations such as removing the right side of the large bowel, gastric bypass, and surgery on the pancreas, stomach or oesophagus. So are conditions including diabetes, scleroderma, coeliac disease, Crohn’s disease, ulcerative colitis, liver disease and neurological conditions such as Parkinson’s disease.

Those are the people a specialist will be thinking about. Someone with years of bloating and changeable bowels and nothing like that in their history is a different case, and it’s where the guidance is firmest.

What does UK guidance say about SIBO breath tests?

The grading in the middle row is worth reading properly. “Strong” is how firmly the guideline’s authors make the recommendation. “Weak” describes the quality of the evidence underneath it. They are confident in the advice while admitting the research is thin.

As I write this, the NHS website has no page on SIBO at all, so most of what you’ll find when you search comes from someone else.

Why don’t UK guidelines recommend the breath test for IBS?

Because in people with IBS it gives too many wrong answers. You drink a sugary solution, breathe into a machine at intervals, and the timing of the gas is used to guess where in the gut the fermenting is happening. It’s an indirect measure. In IBS, food can travel through quickly, so gas from the large bowel can arrive early and pass for a small bowel result. The test can show SIBO when it isn’t there and miss it when it is, and it has produced false positives in healthy people with no symptoms at all.

The 2021 guideline adds three more problems. When researchers took samples directly from the small bowel, the more accurate method, they didn’t find SIBO more often in people with suspected IBS. The common breath test agreed poorly with those direct samples. And a positive breath test didn’t predict who would respond to treatment.

What is established about SIBO, and what isn’t?

Established: SIBO happens, it’s more likely after particular surgery and with particular conditions, and the most accurate test, a sample taken from the small bowel through a thin tube passed down from the mouth, is used in research rather than routine care. Outside research, a gastroenterologist uses your medical history alongside a breath test.

Not established: that SIBO explains most IBS, that a breath test can tell the two apart in someone with IBS, or that a positive result means a treatment will work. Researchers still need better tests to separate SIBO from IBS.

Why do some clinics say the NHS is missing SIBO?

The pages pushing SIBO testing often belong to businesses that sell the test, and a business selling breath tests has an interest in telling you your IBS was a misdiagnosis. That doesn’t make every practitioner wrong. It’s worth knowing who is talking before you pay.

There’s a cost beyond money too. A SIBO label on someone with IBS can narrow the conversation to one kind of treatment, when IBS has many options. I’ve written about the same pattern with intolerance testing in do food intolerance tests work.

What should I ask my GP instead?

Ask what has been ruled out. When I was diagnosed, the doctor listened to my stomach for a minute, said IBS and prescribed antispasmodics, without a single question about what I ate. If your diagnosis came as fast as mine, it’s fair to ask which tests were done.

For someone who meets the IBS criteria, NICE expects a full blood count, blood tests for inflammation and an antibody blood test for coeliac disease. A sample of your poo may also be checked for infection and inflammatory bowel disease. The whole process is laid out in how IBS is diagnosed in the UK.

Questions worth taking with you:

• Which tests have I had, and is there anything else to rule out?
• Does anything in my history, such as surgery or another condition, make SIBO more likely?
• Could I be referred to a dietitian?
• My symptoms have changed. Do I need to be seen again?

If you’ve asked and still feel brushed off, what to do when you don’t feel heard has the words for that conversation. And if you’d like help working out where to start with your own week, try the which book quiz.

When not to wait

Some symptoms need a GP quickly, whatever label you’ve been given. 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, or you have shortness of breath, noticeable heartbeats (palpitations) and skin that’s paler than usual.