SIBO Breath Test – 3 Hour (Hydrogen & Methane)
The SIBO 3-Hour Breath Test measures exhaled hydrogen and methane at intervals over three hours after a fermentable substrate to assess small intestinal bacterial overgrowth and intestinal methanogen overgrowth. A hydrogen rise of at least 20 ppm above baseline within 90 minutes indicates SIBO, and methane of at least 10 ppm at any point indicates methanogen overgrowth, by North American…
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Biomarkers
Breath
Sample
5–7 business days
Turnaround
Yes — typically a 12-hour fast following a restricted preparatory diet the day before # REVIEWER FLAG: Confirm exact fasting duration and preparatory-diet instructions with Genova.
Fasting
What is the SIBO 3-Hour test?
The SIBO 3-Hour Breath Test measures exhaled hydrogen and methane at intervals over three hours following ingestion of a fermentable substrate, providing a non-invasive assessment for small intestinal bacterial overgrowth and intestinal methanogen overgrowth. Because hydrogen and methane in the gut arise from microbial fermentation rather than human metabolism, their appearance and timing in the breath reflect the location and extent of bacterial and archaeal activity. In the diagnostic landscape, breath testing is the most widely used non-invasive method for assessing SIBO, with jejunal aspirate culture regarded as a more direct but invasive and less practical alternative. The 3-hour duration captures both early small-intestinal fermentation and later transit, and dual measurement of hydrogen and methane allows detection of both hydrogen-predominant SIBO and methane-predominant overgrowth. Practitioners order it in the workup of bloating, altered bowel habit, and unexplained gastrointestinal symptoms, interpreting results against consensus rise and positivity criteria. The method has recognised limitations in sensitivity and specificity, and results are read alongside the clinical picture.
What does the SIBO 3-Hour test measure?
Hydrogen is not produced by human cells; in the gut it is generated exclusively by bacterial fermentation of carbohydrate. After ingestion of a test substrate, fermentation by small-intestinal bacteria liberates hydrogen, which diffuses into the bloodstream and is exhaled, allowing serial breath sampling to track fermentation over time. An early rise suggests fermentation occurring proximally in the small intestine rather than the colon.
An early and significant rise in breath hydrogen after a fermentable substrate supports excessive bacterial fermentation in the small intestine, the basis for a SIBO diagnosis. The magnitude and timing of the rise, interpreted against consensus criteria, distinguish small-intestinal from normal colonic fermentation. Hydrogen-predominant patterns are associated clinically with diarrhoea-type presentations.
Methane is produced by archaea, principally Methanobrevibacter smithii, which consume hydrogen and generate methane. Because methanogens use hydrogen, a methane-predominant pattern can suppress measured hydrogen. Methane is exhaled and measured on the same breath samples, and an elevated level at any time-point reflects an overgrowth of methanogenic organisms rather than a purely small-intestinal location.
Elevated breath methane indicates intestinal methanogen overgrowth (now often termed IMO), which is clinically associated with constipation-predominant presentations and can occur in the small or large bowel. Because methanogens consume hydrogen, methane positivity is interpreted in its own right and not solely by the rise-over-baseline logic applied to hydrogen.
Why is the SIBO 3-Hour test ordered?
- Investigation of suspected small intestinal bacterial overgrowth in patients with bloating, distension, and altered bowel habit
- Assessment of patients with irritable bowel syndrome-type symptoms where SIBO is considered a contributing factor
- Evaluation of constipation-predominant presentations where intestinal methanogen overgrowth (methane positivity) is suspected
- Investigation of unexplained chronic diarrhoea where hydrogen-predominant overgrowth is in the differential
- Assessment in patients with predisposing conditions — prior gastrointestinal surgery, dysmotility, structural abnormalities, or chronic proton pump inhibitor use
- Evaluation of malabsorption or unintended weight loss where bacterial overgrowth is being excluded
- Re-testing to assess response after antimicrobial or prokinetic treatment for confirmed overgrowth
Sample collection and turnaround
Sample type
Breath
Fasting required
Yes — typically a 12-hour fast following a restricted preparatory diet the day before # REVIEWER FLAG: Confirm exact fasting duration and preparatory-diet instructions with Genova.
Collection method
At-home collection kit
Turnaround
5–7 business days
Collection notes
Requires a restricted, low-fermentable preparatory diet the day before and a fast (commonly 12 hours) beforehand. A baseline breath sample is collected, the test substrate is ingested, and breath samples are taken at set intervals over three hours. Avoid antibiotics for the recommended washout period, and avoid smoking, eating, and vigorous exercise during the test. # REVIEWER FLAG: Confirm full collection protocol, substrate, and sampling intervals with Genova Diagnostics before publication.
Specimen requirements
Breath samples collected into the kit-provided tubes at the specified intervals. # REVIEWER FLAG: Confirm tube type, number of samples, and stability/shipping requirements with Genova.
What can affect SIBO 3-Hour results?
Residual fermentable carbohydrate from the day before raises baseline and early gas production, causing false-positive patterns. A restricted preparatory diet the day before is required.
Failure to fast for the specified period leaves fermentable material in the gut, elevating baseline readings and confounding the rise-over-baseline interpretation.
Antibiotics within the preceding weeks suppress the bacterial populations being assessed, producing false-negative results. A washout interval (commonly around four weeks) is advised. # REVIEWER FLAG: Confirm Genova's recommended antibiotic washout interval.
Agents that alter transit change the timing of substrate delivery to fermenting organisms, distorting the curve. Recent colonoscopy preparation can transiently alter the microbial picture.
Smoking and vigorous exertion during sampling can alter breath gas concentrations independent of intestinal fermentation and should be avoided during the test.
Fast transit can deliver substrate to the colon early, mimicking a small-intestinal rise, while slow transit can blunt or delay the curve, complicating interpretation. # REVIEWER FLAG: Note substrate choice affects this — confirm lactulose vs glucose handling.
What do SIBO 3-Hour results mean?
Elevated
An early rise in hydrogen of at least 20 ppm above baseline within 90 minutes is consistent with hydrogen-predominant SIBO, while a methane level of at least 10 ppm at any point indicates intestinal methanogen overgrowth. Either pattern, in a compatible clinical context, supports overgrowth and may guide antimicrobial or prokinetic management.
Normal
Curves remaining below the consensus rise and positivity thresholds are interpreted as a normal result. Because both false negatives and false positives occur, a normal study is read alongside symptoms, and persistent strong clinical suspicion may justify reassessment or alternative evaluation.
Reduced
Low, flat hydrogen and methane curves indicate the absence of significant abnormal fermentation by the criteria applied. A negative result reduces the likelihood of overgrowth but does not entirely exclude it, given the test's limited sensitivity.
Note: Breath testing for SIBO has acknowledged limitations in sensitivity and specificity, and interpretation depends on the substrate used, the preparatory diet, and adherence to fasting. Lactulose and glucose substrates yield different performance characteristics, and rapid transit can mimic a positive small-intestinal rise. Results must be interpreted against the stated consensus criteria and the clinical picture, never as a standalone diagnosis. # REVIEWER FLAG: Confirm substrate and the exact diagnostic criteria Genova applies for this 3-hour panel.
Frequently asked questions
It measures exhaled hydrogen and methane at intervals over three hours after ingesting a fermentable substrate. Because these gases come from microbial fermentation rather than human metabolism, their pattern reflects bacterial and methanogen activity in the gut.
How to access the SIBO 3-Hour test
The SIBO 3-Hour 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: June 3, 2026
Last reviewed: June 3, 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)
- Ghoshal UC. How to interpret hydrogen breath tests. J Neurogastroenterol Motil. (2011)
- Saad RJ, Chey WD. Breath testing for small intestinal bacterial overgrowth: maximizing test accuracy. Clin Gastroenterol Hepatol. (2014)
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.