Graphic of person breathing out molecules of hydrogen and methane

Digestive Health Breath Test FAQs

Find out more about hydrogen methane breath tests

Preparing for your Hydrogen Methane Breath Test

What can I eat before doing the test?

At least 24 hours before starting the test you will need to limit your diet to the foods listed below. For the last 12 hours before starting the test you will need to fast completely (no food or drink).

If you normally do not eat any of the foods on the list then you will need to fast for the full 24 hours before the test.

Foods you can eat on the limited diet are:

  • plain white bread (including gluten-free) – all forms of bread (baguettes, rolls etc.) and toast are allowed
  • plain white rice
  • plain white potatoes (no skin)
  • baked or grilled white meat or fish (no oily fish, no skin)
  • plain tofu
  • a maximum of two eggs
  • water
  • non-flavoured black coffee or
  • black tea (no milk, no herbal teas)
  • only salt may be used to flavour your food.
  • a little butter, oil or margarine is permitted (1tsp)

No other foods or drinks are allowed.

Milk and milk substitutes including oat, almond, rice and soya milks are not permitted.

Do I need to fast before the test?

You should fast for at least 12 hours before the test. Before fasting, you will also need to eat only a limited low-fermentable diet for at least 12 hours.

Once I start the test can I eat and drink?

You cannot eat during the test, but you can have small sips of water.

What if I make a mistake and eat food I’m not supposed to?

You should only eat the foods listed above on the day before the breath test. This is to make sure the bacteria in your gut are producing as little gas as possible when you start the test (to ensure your results are accurate).

If you eat something that is not on the list, you risk getting an invalid test result and you may have to pay for another breath test.

Do I need to stop or change medication before doing the test?

Some medications can affect the results of the test so you should avoid taking them before the test. These include:

Oral antibiotics Do not take for at least 4 weeks before the test

Laxatives & Pro-motility drugs (e.g. domperidone), this also includes magnesium supplements

Stop at least 1 week before the test
Probiotics (Bacterial supplements), including probiotic drinks and yoghurts. Stop at least 1 week before the test
Anti-diarrhoea medication (e.g. Imodium) Stop at least 2 days before the test
Gaviscon Can interfere with the test process. Do not take from 24 hours before the start of the test until the test is complete.

If you require any of the above medications and feel unable to stop them for the required time, please consult the doctor that referred you for testing before doing the test. We are unable to provide specialist advice on how these medications may affect your results. All other medications can be taken as normal, this includes:

  • Acid reflux medications (e.g. PPIs such as omeprazole, esomeprazole, lansoprazole, and H2A receptor antagonists such as famotidine, cimetidine)
  • Topical antibiotics (e.g. creams)
  • Antifungals
  • Vitamin & herbal supplements (except magnesium – see above)
  • Medications unrelated to gut health, such as statins, beta-blockers, anti-depressants, anti-histamines, inhalers, pain killers

Can I still do the test if I am unwell?

If you’re feeling unwell it is best to postpone the test until you are feeling better.

During the Breath Test

Are there any risks associated with this test?

There are no risks involved in performing your test, you may experience some of your usual digestive symptoms during the test, this is normal.

What does the test involve?

You will provide an initial breath sample by blowing into a test tube through a straw. This will give us your baseline reading.

Then, you will drink water containing a carbohydrate (lactulose, glucose, fructose or lactose) which needs to be drunk within a minute or two.

Breath samples then need to be taken at regular intervals over 2-4 hours (depending on which test you are doing), to monitor how your gut responds. Along with the samples, you will record any symptoms experienced using the symptom form provided, this helps your doctor to analyse your results.

What are the different kits?

We offer four different home breath tests for gut health. Lactulose and glucose tests can be used to help diagnose small intestinal bacterial overgrowth (SIBO). Lactose and fructose tests can be used to detect intolerances to milk sugars or fruit sugars respectively.


What is included in the test kits?

The kit contains everything needed to do the test (just add water):

  • Test tubes (6 or 10 depending on test)
  • Straw
  • Substrate (lactulose, glucose, lactose or fructose depending on the test)
  • Labels
  • Symptom sheet
  • Instruction leaflet
  • Freepost envelope to post back for analysis

How long does the test take?

Collecting each sample will take less than a minute. You will need to collect several samples at specific times over a period of 2-4 hours. Read the instructions provided with your test carefully before starting.

Do I have to drink the substrate solution as part of my breath test?

Yes. Each kit contains a sugar substrate (whether your test contains lactulose, glucose, lactose, or fructose) that you should dilute in water and then drink at the correct point during the test.

This is a very important step, failure to drink the whole sugar substrate diluted in a glass of water will make your test invalid.

How do I collect a breath sample?

Your test will contain several collection tubes and a straw. For each sample, unscrew the lid and put one end of the straw in the collecting tube. Blow through the straw into the tube for 3-5 seconds until you see condensation forming on the inside of the tube. Immediately screw the lid back on (not too tightly).

Watch our video for full instructions:

Can I take more than one breath test on the same day?

No. If you have been asked to take more than one test, e.g. lactose and fructose, you should do each test on a different day. You will need to follow the limited diet and 12 hour fast before each test. Taking two tests on the same day will produce invalid results.

How does the test work?

Breath tests for digestive health detect small amounts of hydrogen and methane gases in your breath. Our bodies cannot produce these gases themselves. Instead they are made by micro organisms living in our intestines, and the amount of hydrogen and methane they produce provides valuable insights into your gut health.

In SIBO, the extra bacteria in your small intestine are able to use the sugars that you eat before your body absorbs it. These bacteria, along with other micro organisms, convert the sugar into hydrogen and methane.

In food intolerances, the sugars you’re intolerant to don’t get absorbed efficiently by your body, so there is plenty available for the micro organisms that live in your large intestine to convert into hydrogen and methane.

A lot of the hydrogen and methane escapes your body as flatulence or belching but some is absorbed into your blood. The hydrogen and methane in your blood is released in your lungs and can be measured on your breath with a breath test.

Breath tests are a simple and safe way to collect these gases from your breath to start understanding your symptoms. This forms part of the information that a specialist doctor can use to help you to take better control of your gut health.

Watch our video to find out more:

Is lactulose going to give me diarrhea?

The Lactulose SIBO Breath Test contains lactulose, which is also sometimes used as a laxative. This test only uses a very small amount of lactulose and most people typically don’t experience any symptoms outside their normal range.

A small number of patients may experience diarrhoea, but this should be mild and short lived. If your symptoms persist, you should contact your referring doctor.

How long are the samples valid for?

The breath samples are stable for up to two weeks and across a wide temperature range (-20°C to 40°C). Samples received after two weeks of collection may be invalid.

About the Breath Test Process

When will I get my results?

Once the kit arrives back at our lab, the results will typically be available within 2-3 working days.

How will I get my results?

If you are a private patient the results will be emailed to you and the doctor that referred you. If you are an NHS patient, please contact the hospital that referred you for the results.

Why do I need to be referred by my doctor?

We require a referral for hydrogen and methane breath tests because if the test leads to a positive result, then it may require specific medical or dietetic treatment from a healthcare practitioner.

How is the test analysed?

The test is analysed by a state-of-the-art gas chromatography system, which measures hydrogen, methane, and carbon dioxide levels in line with recommendations by the UK and North American Consensus on Hydrogen and Methane-based Breath Testing.

Where is analysis done?

The breath tests are analysed at our laboratory by trained gas chromatography scientists and clinical physiologists.

What is the difference between glucose and lactulose in the SIBO Breath Tests?

We provide two different tests that can help to diagnose small intestinal bacterial overgrowth (SIBO). Each test contains a different sugar substrate, either lactulose or glucose.

Lactulose tests are the most commonly used. Your body does not absorb lactulose so it can be used to detect SIBO at any point in your small intestine. But, because the lactulose is still present in your colon/large intestine, the test can sometimes give a positive result even if you don’t have SIBO.

Some people who get a positive result from Lactulose tests, may be asked to take a glucose test too. You may also be asked to take a glucose test if there are other reasons why a lactulose test may not work. Glucose is absorbed by your body in the first third of the small intestine, so it can only detect SIBO in that region. It will not detect SIBO if it is in lower parts of your digestive system. If you get a positive result from this test, then it is very likely that you do have SIBO.

For Healthcare Professionals

How much do tests cost?

Tests are available to the NHS at costs below the NHS tariff. For private tests, insurance companies can be billed directly.

How can I start using breath tests with my patients?

You can buy HMBT test kits directly from us, which you can then give to your patients. Alternatively, you can refer patients to the Functional Gut Clinic for testing and they will manage the complete process including sending out kits, performing analysis and reporting results.

To get started, contact us via this form.

Can the kits be used by the NHS?

HMBT UK mapYes. There are several NHS hospitals already using the kits as they have significant benefits for both patients and the hospital:

  • Test can be done at home or in an outpatient setting if preferred
  • No capital outlay or ongoing maintenance costs
  • Reduced waiting lists
  • Reduced staff burden
  • Test cost is well within the NHS tariff

Is home testing a good alternative to in-clinic HMBT?

Replacing in-clinic tests with at home testing saves time and reduces COVID-19 risks for patients by reducing the number of required clinical consultations. Tests can be performed at the patient’s convenience. Test costs are below the NHS tariff and results are returned rapidly together with specialist interpretation.

A recent quality review showed that over 95% (1457/1518 lactulose tests) of home breath tests were performed successfully and returned reliable results. There was a 0.1% rate of patient error.

Are there any additional risks to home testing?

Home testing is viable, safe and efficient.

>90% of issues with home test results do not affect reliability and can be overcome by slight changes to the analysis process. Invalid baseline samples can be substituted with a surrogate sample. Analysis of time courses with invalid 90 minute samples can be done using 75 minute samples instead. High baseline samples can be re-collected subsequently.

A small number of issues result from patient errors such as failures to follow protocols or label samples correctly.

What reporting criteria do you use for SIBO?

There are two main consensus documents that people follow when interpreting SIBO breath test results, the North American Consensus 2017 and the European Guidelines. The Functional Gut Diagnostics team have completed a comparison of these two approaches to assess their relative outcomes.

European SIBO cut off values ≥ 10 ppm rise in hydrogen above baseline within 60 minutes.

North American SIBO cut off values ≥ 20 ppm rise in hydrogen above baseline within 90 minutes.

We provide a report using both the above as consultants have their own preferences as to which parameters they prefer to use.

Most patients come out either positive for both parameters or negative for both parameters, but in instances where the results are conflicting, we will look at patient symptoms during the test to inform the borderline result or recommend a follow-up glucose test to provide clarity.

I have a different question.

If you have questions that aren’t answered here, then please contact us: 

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