How the SIBO breath test is performed

If you have bloating, gas, abdominal pain or changes in bowel habits, the SIBO breath test can help guide the assessment of bacterial overgrowth in the small intestine. Its results should be interpreted alongside the preparation, protocol and clinical assessment.

In summary:

• The SIBO breath test measures hydrogen and methane in exhaled air after ingesting a fermentable substrate.
• The preceding diet, fasting, medications and the centre’s protocol can modify intestinal gas production.
• The North American Consensus establishes criteria for assessing increases in hydrogen and methane levels, although it acknowledges limitations in the test.
• A positive result does not, on its own, confirm the cause of symptoms or automatically determine treatment.

The Xenogene SIBO breath test should be requested and interpreted with a healthcare professional, taking into account the method used and the clinical context.

What does the SIBO breath test measure?

The SIBO breath test measures hydrogen and methane in exhaled breath after administering a fermentable substrate, such as glucose or lactulose, to determine whether gas production follows a pattern compatible with bacterial overgrowth in the small intestine.

The substrate is used by microorganisms in the digestive tract during carbohydrate fermentation. Bacteria produce hydrogen; certain methanogenic microorganisms can then use it to generate methane. Measuring both gases therefore provides more information than measuring just one, according to the North American Consensus on breath testing.

Exhaled breath indirectly reflects this intestinal gas production, but it does not, by itself, identify the microorganisms responsible or explain the cause of symptoms. To broaden the assessment, a healthcare professional may consider an intestinal microbiome analysis alongside the clinical history and other tests.

How should you prepare for the test?

Preparation for the SIBO breath test should follow the laboratory’s instructions and the clinical indication. It usually includes a specific pre-test diet, fasting, avoiding certain activities, and reviewing any medicines or supplements that could affect fermentation or intestinal transit, as failing to follow any of these instructions may make the results more difficult to interpret.

Before your appointment, confirm in writing:

• Which foods are allowed the day before and for how long.
• How many hours of fasting are required.
• Whether you should avoid smoking, strenuous exercise or certain activities.
• What to do if you take antibiotics, probiotics, laxatives, prokinetics or antacids.
• Whether there is any clinical circumstance in which the test should be postponed.

Do not stop any treatment on your own: a healthcare professional should assess each case, and the laboratory should provide the applicable protocol. The North American Consensus on breath testing highlights that preparation and methodology influence interpretation. Healthcare professionals can review the indication and protocol through the healthcare professional access.

How is the breath test performed?

The SIBO breath test begins with a baseline exhaled-air sample, followed by the ingestion of glucose or lactulose, and requires further samples at scheduled intervals to observe changes in hydrogen and methane throughout the test.

The usual procedure follows these steps:

1. A baseline sample is collected before the substrate is administered to determine the initial gas levels.
2. The patient drinks the solution specified in the laboratory protocol: glucose or lactulose.
3. Serial exhaled-air samples are collected at the established times, without changing the protocol between collections.
4. The laboratory analyses the concentration of hydrogen and methane and plots their evolution to support clinical assessment.

The number of samples, the interval between them and the total duration must be specified in the protocol used. The North American consensus on breath testing describes general criteria but does not replace the centre’s specific instructions. Other analyses use similar procedures, such as the fructose breath test.

How is it interpreted according to the North American Consensus?

According to the North American Consensus, the result is interpreted by checking whether hydrogen increases by at least 20 parts per million (ppm) during the first 90 minutes or methane reaches 10 ppm or higher at any point, always alongside the protocol used and the clinical assessment.

The hydrogen criterion is intended to identify early gas production compatible with fermentation in the small intestine. Methane, by contrast, is considered a distinct pattern: elevated methane levels may be associated with slower intestinal transit, although they do not explain all symptoms on their own.

These thresholds come from the consensus published in The American Journal of Gastroenterology in 2017 (North American Consensus on breath tests). The document also points out methodological limitations: the substrate, collection times and intestinal transit can affect the interpretation. For this reason, the report should be interpreted alongside other available digestive tests, not in isolation or as an automatic indication for treatment.

What are the limitations of the SIBO breath test?

The SIBO breath test is an indirect test and may produce false-positive or false-negative results because of preparation, the substrate used, intestinal transit and the laboratory method. For this reason, an isolated result does not confirm the cause of symptoms or determine treatment, according to the North American Consensus.

Transit speed can alter when the substrate reaches different areas of the intestine and change the observed gas pattern. In addition, glucose and lactulose do not provide exactly the same information, and laboratories may differ in their protocols, collection times and the gases measured.

Therefore, a positive result may require a review of possible factors that could explain it, while a negative result does not rule out all causes of bloating, pain or changes in bowel habits. Interpretation should take symptoms, medical history, preparation and the method used into account. Where appropriate, the result may be considered alongside an integrated microbiome and function profile, always under the assessment of a healthcare professional.

Frequently asked questions

What is the difference between measuring hydrogen and measuring methane?

Measuring hydrogen and methane provides information about gases produced by different microorganisms during fermentation. Some microorganisms consume hydrogen and produce methane, so analysing both gases can identify patterns that would not appear when measuring hydrogen alone. According to the North American Consensus (2017), methane should also be considered when assessing constipation, although the result requires clinical context.

Can the test be performed while taking antibiotics or probiotics?

The test may be affected by antibiotics, probiotics and other treatments that alter the microbiota or intestinal gas production. They should not be stopped without medical advice: the laboratory and healthcare professional should indicate whether the test needs to be postponed and for how long. The North American Consensus (2017) recognises that preparation influences the result, but it does not replace the instructions for the protocol being used.

What does a positive methane result mean?

A positive methane result indicates that elevated production of this gas has been detected according to the threshold used by the protocol. The North American Consensus (2017) proposes considering a methane level of at least 10 parts per million at any point during the test as positive. This finding may be associated with constipation, but it does not by itself establish its cause or determine treatment.

Does a negative result rule out all digestive problems?

No. A negative result does not rule out all digestive problems, nor does it show that the symptoms have no organic or functional cause. The test indirectly assesses certain gas patterns and may be influenced by the substrate, intestinal transit, preparation and method used. According to the North American Consensus (2017), it should be interpreted alongside the clinical history and not in isolation.

When is it advisable to repeat a breath test?

It is advisable to repeat it only when there is a clinical reason and the healthcare professional considers that the result could change the assessment. It may be considered if preparation was incorrect, the protocol was not completed, new symptoms appear or a discordant result needs to be reviewed. The North American Consensus (2017) does not establish a universal interval: the decision should be individualised and based on a comparable protocol.

Learn more about the SIBO breath test and its technical specifications

Sources

• Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus — Am J Gastroenterol — 2017-05-01