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Hydrogen and methane breath tests: when are they useful?
Bloating is one of the commonest symptoms seen in gastroenterology. Many people ask for a SIBO test after reading that bloating, wind, diarrhoea or constipation can be caused by bacterial overgrowth. That is possible, although these symptoms occur in several other digestive conditions as well.
Hydrogen and methane breath tests can be useful when the clinical history points towards small intestinal bacterial overgrowth or intestinal methanogen overgrowth, although the result still needs to be interpreted alongside the symptoms, previous investigations and quality of the test preparation rather than as a number on its own.
What does the test measure?
Gut microbes ferment carbohydrates and produce gases. Some of this gas passes into the bloodstream, reaches the lungs and can be measured in the breath.
For a SIBO test, a measured dose of lactulose or glucose is taken after a baseline breath sample. Further samples are collected at regular intervals. The timing and size of any rise in hydrogen or methane form the test pattern.
Hydrogen is produced mainly by bacteria. Methane is produced by organisms called methanogens, which belong to a different biological group known as archaea. This is why persistent methane production is now described as intestinal methanogen overgrowth, or IMO, rather than methane-dominant SIBO.
What can hydrogen and methane breath tests help identify?
Small intestinal bacterial overgrowth
An early rise in hydrogen may support a diagnosis of SIBO, particularly when the symptoms and medical history fit. Common symptoms include bloating, excess wind, abdominal discomfort and loose stools.
Intestinal methanogen overgrowth
A raised methane level is associated more often with constipation, hard stools and slower movement through the bowel. Methane can be present throughout the test rather than showing the same early rise as hydrogen.
Carbohydrate malabsorption
Hydrogen and methane testing can also be performed after lactose or fructose to assess whether those sugars are being absorbed properly, but these are separate tests using a different test drink and cannot be inferred from a lactulose SIBO test.
A urea breath test for Helicobacter pylori serves a different purpose, as it looks for a stomach infection and has its own preparation requirements.
Who is more likely to benefit from testing?
Testing is more useful when persistent symptoms are accompanied by a reason to suspect overgrowth. Examples include:
- Previous surgery involving the stomach or small bowel
- A known disorder affecting movement through the gut
- Diabetes with suspected gut-motility problems
- Crohn’s disease, coeliac disease or another condition affecting the small bowel
- Recurrent symptoms after a previous, well-supported diagnosis of SIBO
- Ongoing bloating with diarrhoea or constipation after more common causes have been considered
In my practice, the question is usually whether a breath test is likely to change treatment. Bloating alone does not automatically mean SIBO, and arranging the test without considering the rest of the history can lead to an unhelpful result.
When should something else come first?
A breath test should not delay investigation of symptoms that may point to a more significant problem.
Speak to a doctor before arranging the test if you have:
- Unexplained weight loss
- Blood in the stool or black stools
- Iron-deficiency anaemia
- Persistent vomiting
- Difficulty swallowing
- A new and persistent change in bowel habit
- Symptoms waking you repeatedly at night
- A strong family history of bowel cancer, inflammatory bowel disease or coeliac disease
Depending on the circumstances, blood tests, stool tests, imaging, gastroscopy or colonoscopy may be more appropriate. Online symptom lists cannot make that distinction reliably because several conditions cause the same pattern of symptoms.
How accurate are SIBO breath tests?
Breath testing is useful, but it has recognised limitations. There is no perfect reference test for SIBO, and different centres have historically used different protocols and thresholds.
A rapid transit time can move the test drink into the colon earlier than expected and produce a pattern that resembles SIBO. Slow transit, recent antibiotics, poor preparation or low gas production can give a falsely reassuring result. Standard two-gas tests also do not measure hydrogen sulphide.
Breath testing remains useful when it is considered as part of the clinical assessment, taking account of the shape of the curve, the baseline values, any symptoms during the test and the original reason for requesting it.
How should I prepare?
The preparation is important because food, medicines, smoking and exercise can alter breath gases.
Your provider will send exact instructions. A typical protocol may include:
- Avoiding antibiotics for about four weeks
- Avoiding probiotics, laxatives and medicines that alter gut movement for the specified period
- Following a restricted diet on the day before the test
- Fasting overnight, with water allowed according to the instructions
- Avoiding smoking, vaping, chewing gum and strenuous exercise on the morning
- Waiting for the advised interval after colonoscopy bowel preparation
Do not stop prescribed medication without checking. If you have diabetes, the fasting period and test drink need to be planned safely.
If the preparation has not been followed, tell the provider, as postponing the test may be more useful than producing a result that cannot be interpreted confidently.
What happens during the test?
A baseline breath sample is taken first. You then drink the test solution and provide further breath samples, commonly every 15 to 20 minutes for two to three hours.
There are no needles, sedation or radiation, although the test drink may reproduce bloating, wind, cramping or loose stools for a short time. It is sensible to bring something to read and allow enough time for the full series of samples.
The symptoms recorded during the test can be relevant, although symptoms alone do not decide whether the test is positive.
What happens after a positive result?
What happens next depends on the pattern, the symptoms and the likely reason for the overgrowth, with treatment sometimes involving an antibiotic, management of constipation, dietary changes or treatment of an underlying motility problem. Repeated courses of antibiotics without considering why the problem has developed can lead to repeated relapse.
A positive methane result often shifts attention towards constipation and slow transit. Nutritional blood tests may occasionally be useful whenSIBO has been prolonged or there is weight loss, anaemia or concern about malabsorption.
A clinical review is useful before treatment because borderline results and poorly prepared tests can otherwise lead to unnecessary medication.
What if the result is negative?
A negative result makes hydrogen- or methane-producing overgrowth less likely without necessarily explaining the symptoms, and the history may instead point towards constipation, irritable bowel syndrome, coeliac disease, food-related symptoms, medication effects or another gastrointestinal problem. Further tests are sometimes needed. In other cases, management can begin without another investigation.
Arranging a hydrogen and methane breath test in Milton Keynes
Harmonyoffers hydrogen and methane breath testing for suspected SIBO and intestinal methanogen overgrowth. The test can be arranged after a consultation when the cause of the symptoms is unclear, or directly when there is already a clear clinical reason for testing.
A consultation is often useful when symptoms are persistent, previous tests have been normal or there is uncertainty about whether breath testing will answer the right question. The result can then be interpreted alongside the rest of the clinical picture and used to decide what happens next.
Self-referral is welcome, and appointments are available for self-paying and insured patients
Frequently asked questions
Is a SIBO breath test painful?
No. It involves drinking the test solution and giving repeated breath samples. The solution can temporarily cause bloating, wind or loose stools.
How long does the test take?
Black coffee is usually allowed during the clear-fluid period. Milk, cream and non-dairy creamer are not clear fluids. Follow the list supplied by your unit.
Can a negative breath test completely exclude SIBO?
Pause briefly and try again more slowly. Contact the endoscopy unit if vomiting continues or you cannot keep the fluid down. An incomplete preparation may mean the examination cannot be completed properly.
Is methane the same as SIBO?
Many medicines can be taken with a small sip of water, but blood thinners, diabetes treatment, iron tablets and some weight-loss medicines need specific advice. Check before the day of the procedure.
Is this the same as an H. pylori breath test?
The examination commonly takes 30 to 45 minutes, but admission, consent and recovery add time. Sedation usually means a longer recovery and the need for an escort home.
Can I start antibiotics after a positive result?
The examination commonly takes 30 to 45 minutes, but admission, consent and recovery add time. Sedation usually means a longer recovery and the need for an escort home.
Written and clinically reviewedby Dr Arjun Prakash, Consultant Gastroenterologist and Advanced Interventional Endoscopist
Dr Arjun Prakash provides private gastroenterology consultations in Milton Keynes, including assessment for bowel cancer risk, screening colonoscopy, family history, previous polyps and concerning bowel symptoms.
