trio-smart SIBO Breath Test (Three-Gas: Hydrogen, Methane, Hydrogen Sulfide)
The trio-smart breath test measures hydrogen, methane, and hydrogen sulfide in exhaled breath at timed intervals after substrate ingestion. Adding hydrogen sulfide to conventional two-gas testing identifies sulfate-reducing phenotypes that produce a flat hydrogen tracing because hydrogen is consumed rather than exhaled.
3
Biomarkers
Breath
Sample
5–10 business days
Turnaround
Yes — a restricted low-fermentable diet for approximately 24 hours followed by an overnight fast of 8 to 12 hours is required, since preparatory non-adherence is among the commonest causes of an uninterpretable result
Fasting
What is the trio-smart Breath Test test?
The trio-smart breath test measures hydrogen, methane, and hydrogen sulfide in exhaled breath at timed intervals following ingestion of a test substrate, to assess small intestinal bacterial overgrowth and intestinal methanogen overgrowth. It is ordered in patients with bloating, distension, altered bowel habit, and symptoms consistent with irritable bowel syndrome where an overgrowth phenotype is suspected, and to characterise which gas predominates, since this influences treatment selection. The distinguishing feature of this panel is the addition of hydrogen sulfide to the conventional two-gas measurement, and the rationale is sound rather than promotional. Sulfate-reducing organisms consume hydrogen to produce hydrogen sulfide, so a hydrogen sulfide–predominant patient generates a flat hydrogen tracing that conventional testing reports as negative or non-diagnostic despite ongoing symptoms. Measuring all three gases identifies these patients and distinguishes three phenotypes with differing symptom patterns: hydrogen-predominant, methane-predominant with constipation and slowed transit, and hydrogen sulfide–predominant with diarrhoea and visceral hypersensitivity. The evidence supporting the three components differs and should not be treated as uniform. Methane is the most robustly supported: a level at or above 10 ppm at any timepoint is a recognised consensus criterion, the association with constipation is consistent, and the entity has been formally reframed as intestinal methanogen overgrowth because the responsible organisms are archaea rather than bacteria and the overgrowth commonly involves the colon rather than being confined to the small bowel. Hydrogen is well established but imperfect, since the early-rise criterion is a proxy for small bowel location and rapid oro-caecal transit can produce a positive result without overgrowth. Hydrogen sulfide is the newest component, its thresholds are proprietary rather than consensus-derived, and outcome data linking results to treatment response remain limited. Two broader caveats apply to breath testing as a whole. There is no agreed gold standard for SIBO — jejunal aspirate culture is invasive, poorly standardised, and samples only the proximal small bowel — so breath testing is validated against an imperfect comparator and its true accuracy is difficult to establish. And a positive result supports rather than establishes the diagnosis: results should be interpreted alongside symptoms, predisposing factors such as prior gastrointestinal surgery, dysmotility, or proton pump inhibitor use, and after exclusion of coeliac disease, inflammatory bowel disease, and pancreatic insufficiency, which can produce overlapping symptoms and which carry established management pathways.
What does the trio-smart Breath Test test measure?
Hydrogen is not produced by human cells and arises exclusively from bacterial fermentation of carbohydrate. Following ingestion of a test substrate, hydrogen generated by fermenting bacteria diffuses across the intestinal mucosa into the portal circulation, is carried to the lungs, and is exhaled in measurable quantities. In a normally colonised gut, fermentation occurs predominantly in the colon, producing a late rise; earlier fermentation implies bacterial activity in the small bowel.
Breath hydrogen is the longest-established component of SIBO breath testing and forms the basis of most published experience. Its principal limitation is that the early-rise criterion is a proxy for small bowel location rather than a direct measurement of it: rapid oro-caecal transit can deliver substrate to the colon within the diagnostic window and produce a positive result in the absence of small bowel overgrowth. Substrate choice affects performance, with glucose being more specific but confined to the proximal small bowel and lactulose reaching more distal segments at the cost of specificity.
Methane is produced not by bacteria but by methanogenic archaea, predominantly Methanobrevibacter smithii, which consume hydrogen and carbon dioxide to generate methane. Because methanogens are hydrogen-consuming, a methane-predominant patient may show little or no hydrogen rise. Methane exerts a direct effect on intestinal motility, slowing transit, which explains its strong association with constipation. Methanogen overgrowth is not confined to the small bowel and frequently involves the colon.
Methane is the most robustly supported component of the panel. Elevated methane correlates with constipation-predominant symptoms and with a slower transit phenotype, and a level at or above 10 ppm at any timepoint is the recognised positive criterion. Because the responsible organisms are archaea rather than bacteria and the overgrowth is not limited to the small intestine, the entity has been formally reframed as intestinal methanogen overgrowth rather than as a subtype of SIBO, and this distinction carries treatment implications since methanogens respond differently to antimicrobial therapy.
Hydrogen sulfide is produced by sulfate-reducing organisms, principally Desulfovibrio and Fusobacterium species, which consume hydrogen as a substrate. This consumption is clinically significant for testing: in a hydrogen sulfide–predominant patient, hydrogen is used up rather than exhaled, producing the flat-line hydrogen tracing that conventional two-gas testing reports as non-diagnostic despite ongoing symptoms. Hydrogen sulfide is associated with diarrhoea-predominant symptoms and with visceral hypersensitivity.
Hydrogen sulfide measurement is the genuine novelty of this panel and addresses a real diagnostic gap, since patients with hydrogen sulfide–predominant overgrowth were previously undetected on conventional testing and were left without a biochemical explanation for their symptoms. It is also the least validated component: diagnostic thresholds are proprietary rather than consensus-derived, published outcome data linking hydrogen sulfide results to treatment response remain limited, and the clinical significance of intermediate values is not established. It should be interpreted as an emerging measure that adds information rather than as a validated diagnostic threshold.
Why is the trio-smart Breath Test test ordered?
- Assessment of bloating, distension, and altered bowel habit where an overgrowth phenotype is suspected, after exclusion of coeliac disease, inflammatory bowel disease, and enteric infection
- Characterisation of the predominant gas in patients with suspected overgrowth, since hydrogen, methane, and hydrogen sulfide phenotypes differ in symptom pattern and in response to antimicrobial therapy
- Evaluation of patients with constipation-predominant symptoms where intestinal methanogen overgrowth is suspected, methane being the most robustly supported component of the panel
- Assessment of patients with diarrhoea-predominant symptoms who have previously returned a flat or non-diagnostic hydrogen tracing on conventional two-gas testing, where hydrogen sulfide predominance may explain the discrepancy
- Investigation of patients with recognised predisposing factors — prior gastrointestinal surgery, adhesions, dysmotility, scleroderma, diabetic enteropathy, or prolonged proton pump inhibitor use
- Assessment of patients with irritable bowel syndrome phenotypes who have not responded to standard management and in whom an overgrowth contribution is being considered
- Reassessment following antimicrobial treatment of a previously positive test, using the same substrate and protocol for comparability
Sample collection and turnaround
Sample type
Breath
Fasting required
Yes — a restricted low-fermentable diet for approximately 24 hours followed by an overnight fast of 8 to 12 hours is required, since preparatory non-adherence is among the commonest causes of an uninterpretable result
Collection method
At-home collection kit
Turnaround
5–10 business days
Collection notes
Protocol adherence determines whether the result is interpretable. Follow the restricted preparatory diet for the specified period and complete the overnight fast. Withhold antibiotics and antimicrobials for the washout period specified by the laboratory, and withhold probiotics, laxatives, and prokinetics per protocol. Do not smoke or undertake vigorous exertion before or during the test. Collect the baseline sample before ingesting the substrate and adhere precisely to the sampling schedule, recording actual collection times. Document all medications including opioids and proton pump inhibitors, recent antibiotic courses, bowel habit, and any prior gastrointestinal surgery.
Specimen requirements
Timed exhaled breath samples collected into the devices supplied in the trio-smart kit, per the manufacturer's sampling schedule. Samples must be labelled with actual collection times and returned per the laboratory's transport instructions.
What can affect trio-smart Breath Test results?
Antimicrobial therapy suppresses the organisms responsible for gas production and can produce a falsely negative result, and probiotics alter the fermenting population. A washout period of several weeks after antibiotics is typically required before testing.
Agents that accelerate transit can deliver substrate to the colon within the diagnostic window and produce a falsely positive early rise, while opioids and other agents that slow transit can delay fermentation beyond the sampling period and produce a falsely negative result. These are typically withheld before testing per protocol.
The protocol requires a restricted low-fermentable diet for approximately 24 hours followed by an overnight fast, to clear residual fermentable substrate from the gut. Non-adherence produces an elevated baseline and spurious rises that make the tracing uninterpretable, and this is among the commonest causes of an invalid result.
Smoking alters exhaled gas concentrations directly, and vigorous exertion changes ventilation and gas exchange. Both are prohibited during the test and for a period beforehand, and adherence should be confirmed.
The early-rise criterion assumes that substrate reaching the colon takes longer than the diagnostic window, but rapid transit — particularly with lactulose, which itself accelerates transit — can deliver substrate to the colonic flora within 90 minutes and produce a positive result reflecting normal colonic fermentation rather than small bowel overgrowth.
Glucose is absorbed proximally and offers greater specificity but detects only proximal overgrowth, while lactulose reaches distal segments and the colon with correspondingly lower specificity. Sampling intervals, test duration, and thresholds also vary between laboratories, so results are not directly comparable between providers or protocols.
What do trio-smart Breath Test results mean?
Elevated
A hydrogen rise of 20 ppm or more above baseline within 90 minutes supports small intestinal bacterial overgrowth, though rapid transit should be considered as an alternative explanation. Methane at or above 10 ppm at any timepoint, including baseline, supports intestinal methanogen overgrowth and correlates with constipation and slowed transit; because methanogens are archaea and frequently colonise the colon, this is distinct from bacterial small bowel overgrowth and responds differently to antimicrobial therapy. An elevated hydrogen sulfide result suggests a sulfate-reducing phenotype associated with diarrhoea, though its thresholds are proprietary and not consensus-endorsed, so it should be weighted as supportive rather than definitive. Any positive result supports rather than establishes the diagnosis and should be interpreted with symptoms and predisposing factors.
Normal
A negative test does not exclude overgrowth. False negatives arise from recent antimicrobial use, slowed transit delaying fermentation beyond the sampling window, distal overgrowth not reached by the substrate, and protocol non-adherence. Where clinical suspicion remains high after a negative result, consider repeat testing with an alternative substrate after an appropriate washout, and reconsider alternative diagnoses including coeliac disease, inflammatory bowel disease, pancreatic insufficiency, and bile acid diarrhoea.
Reduced
Not applicable in the conventional sense. Low or absent gas production across all three gases indicates that no fermentation pattern meeting diagnostic criteria was detected during the sampling period.
Note: The three components differ substantially in evidential support: methane is the most robustly validated with a consensus threshold, hydrogen is established but relies on an early-rise proxy vulnerable to transit variability, and hydrogen sulfide thresholds are proprietary and lack consensus endorsement or outcome data. Breath testing as a whole is an indirect proxy validated against an imperfect comparator, since no agreed gold standard for SIBO exists. Results depend heavily on preparatory diet adherence, medication washout, and substrate choice, and are not comparable between laboratories using different protocols. A positive result supports rather than establishes the diagnosis, and alternative conditions with overlapping symptoms should be excluded first.
Frequently asked questions
It measures hydrogen, methane, and hydrogen sulfide in exhaled breath at timed intervals after substrate ingestion, to assess small intestinal bacterial overgrowth and intestinal methanogen overgrowth and to identify which gas predominates.
How to access the trio-smart Breath Test test
The trio-smart Breath Test reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: July 16, 2026
Last reviewed: July 16, 2026
- Rezaie A, et al. Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus. Am J Gastroenterol. (2017)
- Pimentel M, et al. ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth. Am J Gastroenterol. (2020)
- Villanueva-Millan MJ, et al. Methanogens and Hydrogen Sulfide Producing Bacteria Guide Distinct Gut Microbe Profiles and Irritable Bowel Syndrome Subtypes. Am J Gastroenterol. (2022)
- Takakura W, Pimentel M. Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome — An Update. Front Psychiatry. (2020)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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