Fiona Lawson | 12 Feb 2024 | SIBO

SIBO Test – All Your Questions Answered (2024)

SIBO is confusing. You’ve heard that this condition—Small Intestinal Bacterial Overgrowth—might be contributing to your IBS or other symptoms, but you’re not sure how to go about addressing it.

There are several different tests for SIBO out there and it’s hard to know which one is best for you. It can also be difficult to get your head around how SIBO tests work.

This article talks you through the different types of SIBO tests, why they work, how to carry out a SIBO test at home and what to do if the test comes back positive.

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What is a SIBO Test?

Who should be tested for SIBO?

How to test for SIBO

How does a SIBO breath test work?

Which SIBO breath test is best?

Is SIBO breath testing reliable?

How to prepare for a SIBO test

How much is a SIBO test?

Where to order a SIBO test

How to test for SIBO at home

How to read and interpret SIBO test results

What does a positive SIBO test mean and what to do next?

What to do if SIBO results are negative


What is a SIBO Test?

As the name suggests, Small Intestine Bacterial Overgrowth (SIBO) is a condition in which bacteria move from the large intestine (where they should be) to the small intestine (where they shouldn’t be).

In the small intestine, the bacteria ferment the carbohydrates we eat and release gas as a by-product. They also eat some of the nutrients from our food. Together, these can lead to uncomfortable symptoms, including:

  • Bloating
  • Abdominal pain
  • Belching
  • Flatulence
  • Nausea
  • Fatigue
  • Brain fog
  • Fatty stools

It’s estimated that up to 15% of people have SIBO, and it’s now believed to be the leading cause of IBS1. However, because the symptoms are non-specific, you can only be sure you have SIBO if you take a test.

A SIBO test looks at either the bacteria the small intestine or the gases they produce to determine if overgrowth is a problem.

Who should be tested for SIBO?

Anyone who’s experiencing the symptoms listed above may want to test. SIBO has also been linked with the following conditions:

  • Irritable Bowel Syndrome (IBS)
  • Fibromyalgia
  • Acne rosacea
  • Chronic fatigue syndrome
  • Ulcerative colitis
  • Hypothyroidism

That’s not to say SIBO is causing these conditions, but studies have found that SIBO and these conditions often co-occur2. For that reason, anyone suffering from the above would also benefit from taking a SIBO test.

How to test for SIBO

SIBO testing is specialised and not readily available on the NHS. If you want to test for SIBO in the UK, you have three options:

  • Small intestine aspiration and quantitative culture

This is a fancy way of saying ‘taking some bacteria from the small intestine and growing it in a petri dish’. This usually takes place in a research setting and is considered the gold standard of SIBO testing3. But it comes with some challenges:

  1. Results are easily skewed, because bacteria from the large intestine can contaminate the sample.
  2. Some bacteria can’t be grown in a petri dish, which can further make the sample misleading.
  3. It’s prohibitively expensive.

These challenges mean this method of testing is rarely used in a clinical setting.

  • Organic acids

This involves weeing in a cup and sending your urine off to be analysed. A specific biomarker that’s looked at—4‐hydroxyphenylacetic acid—is considered to indicate SIBO if it’s raised4.

This method is much easier but, like the small intestine aspiration and quantitative culture, results can easily be skewed.

  • SIBO breath test

This is the simplest, most accessible way to test for SIBO5. People used to have to visit a specialist lab to carry out the test, but new technology means it’s now possible to use a SIBO test kit in your home.

After a day of preparatory eating and a 12-hour fast, you drink a sugary solution. You then collect a sample of your breath by breathing into special tubes at timed intervals for 2.5 hours. You pop the tubes in the post, and a lab analyses your breath to determine whether you have SIBO or not.

How does a SIBO breath test work?

The SIBO breath test works on the principle that bacteria ferment carbohydrates and release gas as a by-product. Two of the gases they release are hydrogen and methane.  

You expel 80% of this gas through your intestines, but the other 20% is absorbed into your blood and travels round to your lungs—where you breathe it out6. By measuring the levels of gases in your breath, a lab can therefore approximate the degree of bacterial overgrowth.

That last part is an important point—the lab aren’t measuring the actual bacteria, but using the gas as an indication of the type and volume of bacteria. Some SIBO breath tests only measure hydrogen, but it’s better to measure hydrogen and methane to get a more accurate picture of potential overgrowth. Here at Healthpath, we perform a hydrogen and methane SIBO test.

Which SIBO breath test is best?

As well as measuring different gases, some tests use different forms of sugary solution. The two main sugars used are glucose and lactulose, and they each come with their own upsides and downsides. Let’s take a look at both:

Glucose. This is a monosaccharide (the smallest unit of carbohydrate).

Upside: Glucose is absorbed in the upper part of the small intestine, which means it doesn’t often reach the colon (large intestine). Since colonic fermentation is unlikely to interfere with the results, a SIBO breath test using glucose will rarely give false positive results7.

Downside: The fact that glucose is absorbed in the upper part of the small intestine can also be a downside—because it may not reach the lower part of the small intestine, where SIBO is more likely to be. This can lead to false-negative results.

Lactulose. This is a non-absorbable sugar made from lactose.

Upside: As this sugar is non-absorbable, it travels all the way through the small intestine. This means it’s much less likely to give false negative results8.

Downside: If the lactulose travels through the small intestine too quickly (if a person has diarrhoea, for example), it can be more prone to giving false-positive results. Despite its name, lactulose is not lactose, so is usually fine for people who are lactose-intolerant to take. However, if you have a true lactose allergy (which is rare) then you should use glucose instead.

Lactulose is a synthetic sugar that is made in a lab. It is not digested or absorbed by human cells: that’s why we use it in a SIBO test. It travels the length of the small intestine and ends up in your colon. There are some examples in the medical literature where children with severe milk allergies have reacted to lactulose, so if you’re worried, ask for glucose as a replacement.

Find out if you have SIBO.

View our at home SIBO test

Is SIBO breath testing reliable?

As you can see, no test is perfect. Healthpath’s SIBO breath test uses lactulose because, in our practitioners’ experience, it gives a better overview.

“A breath test using glucose has value,” says Healthpath Nutritional Therapist, Fiona Lawson, “but lactulose can identify SIBO throughout the small intestine, which is more useful.”

However, the main limitation of any type of SIBO breath testing is that it can’t always distinguish between gases from the small intestine and gases from the large intestine. For this reason, SIBO breath tests are most useful when interpreted by a skilled practitioner, as they consider your symptoms in conjunction with your test data.

What’s more, SIBO breath tests can’t measure all the gases. Most people with SIBO either produce mostly hydrogen, mostly methane or mostly hydrogen sulphide (more on this below). At present, there’s no way to test for hydrogen sulphide—so receiving practitioner input is again important9.

As with many tests, you also increase your chances of receiving a reliable test result if you prepare properly.

How to prepare for a SIBO test

Says Functional Medicine Practitioner, Alex Manos, “Diagnostic accuracy of hydrogen breath testing for SIBO can be maximised by careful patient selection for testing, proper test preparation, and standardisation of test performance and test interpretation.”

An at-home SIBO breath test is designed to make testing easy—and a good test kit should guide you through the preparatory stages10. These include:

4 weeks before the test: finish taking any antibiotics. You should never stop a course of antibiotics in order to take a test—talk to your GP first.

1 week before the test: if tolerated, stop any promotility drugs and laxatives. Again, you must never stop taking drugs without first consulting your doctor.

1 day before the test: avoid all complex carbohydrates and fermentable foods. These can interfere with the test results.

12 hours before the test: fast and drink only water. Most people find it easy to do a SIBO breath test first thing in the morning, so they can fast overnight.

On the day of the test: avoid smoking and physical activity before and during the three-hour test period.

How to prepare for SIBO test infographic

How much is a SIBO test?

The number of NHS hospitals offering SIBO breath testing is growing. You may find that you can get a test and treatment through your GP, who will refer you to a gastroenterologist. However, the NHS trust in your area may not yet offer SIBO testing. Or, your local hospital may only offer a hydrogen test, meaning that if you have methane SIBO, you’ll get a false negative result.

Many people find it more convenient to pay for a SIBO test privately.

Most SIBO breath tests cost between £90–£200. But it’s important you do your research. Find out whether the lab or online supplier uses glucose or lactulose in the test, and whether they test for both hydrogen and methane. You also want to know if they’ll help you understand the results.

The Healthpath SIBO breath test costs £185. This includes all test materials, results and an easy-to-understand report written by a qualified practitioner.

Where to order a SIBO test

You can find a private medical lab that offers SIBO breath tests, or you can order a SIBO breath test online. There are several websites who sell the test but, as mentioned, make sure you check that it’s a reliable company first.

You can order a SIBO breath test by visiting the Healthpath shop.

what type of diet for a sibo test

How to test for SIBO at home

If you’ve ordered a home test kit for SIBO online, the test kit will be delivered straight to your door.

Choose a day to take the test—most people find it easiest to do it on a weekend, as they can set aside a day to prepare and then a morning to do the test. Follow the preparatory information to make sure your test results are as accurate as possible.

To take the test, first give a baseline breath sample using the kit provided. Then drink the sugary solution, and wait 30 minutes.

After 30 minutes, give another breath sample in a second tube. Repeat this process at the specified time intervals for a total of 2.5 hours. You’ll end up with seven breath-filled tubes in total, which you can then send off to the lab for interpretation.

Following a SIBO test, you can resume your normal diet while you wait for the results. You should get your results back within 14 working days.

How to read and interpret SIBO test results

As lots of labs test for SIBO, in the past there has been a confusing lack of standardisation for results. A group of experts met in 2017 to agree on some guidelines, which were summarised in ‘The North American Consensus’11

In the consensus, the experts agreed on the following:

Positive for hydrogen-predominant SIBO. If there is a rise in hydrogen of 20 p.p.m. (parts per million) from baseline within 90 minutes, this is considered positive for hydrogen-predominant SIBO.

Positive for intestinal methanogen overgrowth. A level of at least 10 p.p.m at any time is considered positive for intestinal methanogen overgrowth.

There’s currently no way to test for hydrogen-sulphide predominant SIBO specifically, so this is usually determined by a process of elimination. If both hydrogen and methane are very low throughout the three hours, this may indicate hydrogen sulphide is present.

On a Healthpath SIBO breath test report, we make it easy to interpret if hydrogen sulphide is present—and we show you what to do about it.

Find out if you have SIBO.

View our at home SIBO test

What does a positive SIBO test mean and what to do next?

You can be positive for either hydrogen or methane, or you can have suspected hydrogen sulphide. In all cases, if you’ve tested positive, you know you have bacteria where they shouldn’t be.

You not only want to get rid of these troublesome bacteria—but you also want to improve the ‘terrain’ of the digestive system as a whole. This requires a multi-pronged approach and the specifics of the treatment will vary by individual.

Here are some guidelines to get you started:

1. Follow a low fermentable-carbohydrate diet

Fermentable carbohydrates—found in some grains, pulses, fruits and vegetables—feed bacteria. It’s a good idea to cut down or eliminate these types of foods for six to eight weeks to ‘starve’ the overgrowth12.

There are several diets that are designed to do this, such as the low-FODMAP diet, the Specific Carbohydrate Diet and the Bi-Phasic Diet. Here at Healthpath, we’ve also provide a SIBO diet guide with the Modified Healthpath Plate.

Whichever diet you choose to help with your SIBO symptoms, it’s important you personalise it. It’s also vital that you don’t stay on this type of diet for a long period of time, because it can have a negative effect on your microbiome.

2. Take antimicrobials

You can take antibiotics to get rid of bacterial overgrowth, but studies have found that natural antimicrobials are equally (if not more) effective13.

The specific antimicrobials you’ll need to take will vary depending on whether you have hydrogen, methane or hydrogen sulphide-predominant SIBO, but common choices include oil of oregano, berberine, neem and garlic.

Like the low-fermentable carbohydrate diet, you shouldn’t take antimicrobials for extended periods of time. For most people, eight to 10 weeks is usually sufficient. And remember: supplements are designed to complement (not replace) a good diet.

3. Consider prebiotics and probiotics

Certain types of prebiotic fibre can help to alleviate methane-predominant SIBO14. Probiotics can also be used to tackle SIBO—and help stop it from re-occurring post-treatment.

But it’s essential to choose the right probiotic supplement, as certain bacterial species could end up making SIBO symptoms worse.

Studies suggest that the species Lactobacillus casei, Bifidobacterium breve and Bifidobacterium bifidum (amongst others)  are effective against SIBO15. Saccharomyces boulardii—a type of friendly yeast—can be helpful too.

4. Tackle the root cause

All of the above will help to beat back the overgrowth and reduce symptoms. But SIBO has a high rate of re-occurrence because people don’t always address what caused SIBO in the first place.

Your body has protective mechanisms in place to ensure SIBO doesn’t occur16. These include:

  • Secretion of hydrochloric acid in your stomach
  • Appropriate gut motility, or the processes and structures that keep food moving through your gut at a suitable rate
  • Production of pancreatic juices and bile, which stop bacteria from reproducing
  • An intact ileo-cecal valve, which acts as the ‘trapdoor’ between your small intestine and large intestine
  • Secretory immunoglobulins—otherwise known as antibodies—which help to destroy errant bacteria

Therefore if SIBO has occurred, one or more of these needs to be addressed. The best way to do with is to work with a qualified Nutritional Therapist or Functional Medicine Practitioner, who is trained to interpret and address imbalances in your body.

What to do if SIBO results are negative

If your test results come back negative, you may be happy to know that you don’t have SIBO. But—if you’re still suffering from symptoms—you may also be confused. You have three options:

  • Re-test. There is a small chance of a test coming back with a false negative, in which case another test may show that you have SIBO after all. This will require paying for a second test, but it can give you peace of mind.
  • Consider testing for something else. SIBO symptoms are non-specific, which means they can also indicate something else. Other conditions with similar symptoms include dysbiosis (an imbalance of bacteria in the large intestine) and carbohydrate intolerance17. By testing your microbiome, such as in Healthpath’s Ultimate Plan Gut Health Test (which costs £399), you can find out if there’s another treatment approach that would suit you better.
  • Speak to a qualified practitioner. They can talk through your unique situation and explain what you can do next. Here at Healthpath, you can speak to one of our Nutritional Therapists or Functional Medicine Practitioners via an online consultation.


Breath testing is currently the easiest, most accessible way to test for SIBO. With the right preparation, it can give an accurate picture of what’s going on in your small intestine.

With Healthpath’s SIBO breath test, you can find out if you have hydrogen-predominant SIBO or methane-predominant SIBO. You can also learn if it’s likely you have hydrogen-sulphide-predominant SIBO.

But test results are meaningless without interpretation, which is why all Healthpath’s tests are reviewed by a qualified practitioner. A Healthpath SIBO breath test report gives you clear explanations, personalised recommendations and extra health tips to help you tackle SIBO effectively.


Fiona Lawson BA (Hons) DipCNM mBANT is a Registered Nutritional Therapist and health writer. She is a member of the Complementary and Natural Healthcare Council (CNHC) and the Institute for Functional Medicine (IFM). As Content Director of Healthpath, Fiona is on a mission to help people take charge of their own health. Read more about Fiona on her practitioner page.



















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