Which breath test measures what
This is the page we would have wanted before spending money on a test.
The short version
The short answer
One breath test measures hydrogen sulfide: trio-smart from Gemelli Biotech, $349 to $369, no prescription needed. The other 4 measure hydrogen and methane only and physically cannot detect the third gas, so a negative from one of them does not rule it out.This matters because of what people do with a negative. A person suspects overgrowth, buys the cheaper test, gets a negative, and concludes the question is settled. It is not settled. It is unmeasured, and those are different things.
| Test | Hydrogen sulfide | Hydrogen | Methane | Price | Prescription |
|---|---|---|---|---|---|
| trio-smartGemelli Biotech · results in 7-14 days | Yes | Yes | Yes | $349–369verified 2026-08-03 | No |
| SIBO 2-hour / 3-hourGenova Diagnostics · results in 10-15 days | No | Yes | Yes | $225–349verified 2026-08-03 | Yes |
| SIBO breath testCommonwealth Diagnostics International · results in 7-10 days | No | Yes | Yes | $295verified 2026-08-03 | Yes |
| QuinTron breath testQuinTron / breathtests.com · results in 5-10 days | No | Yes | Yes | $195–249verified 2026-08-03 | No |
| SIBO breath testAerodiagnostics · results in 7-14 days | No | Yes | Yes | $299verified 2026-08-03 | Yes |
Prices verified on the date shown against each provider’s own page. A price without a date is a claim about today made from memory.
What each test cannot tell you
- trio-smart — Gemelli Biotech
- Measures three gases but cannot tell you what to do about the result. There is no validated hydrogen sulfide threshold in any published guideline; the North American Consensus contains no H2S criterion at all. A number without a threshold is not a diagnosis.
- SIBO 2-hour / 3-hour — Genova Diagnostics
- Does not measure hydrogen sulfide. Infers it from a third-hour flatline, which is an unvalidated inference rather than a measurement. A negative result does not rule out hydrogen sulfide overgrowth.
- SIBO breath test — Commonwealth Diagnostics International
- Does not measure hydrogen sulfide, and says so plainly on its own site.Their own site: “no diagnostic technology on the market can test for H2S at levels of parts per billion”
- QuinTron breath test — QuinTron / breathtests.com
- Does not measure hydrogen sulfide. Direct to consumer with no clinician required, which also means no clinician interprets the result for you.
- SIBO breath test — Aerodiagnostics
- Does not measure hydrogen sulfide. We do not link directly to their storefront; order through a clinician or the provider's main site.
Not a SIBO test
These devices come up constantly in the same conversations. They measure something real. They do not answer the same question, and we do not list them above because doing so would imply they do.
- FoodMarble AIRE 2 $269 (verified 2026-08-03)
- A personal fermentation tracker, not a diagnostic test. No CLIA lab, no timed consensus protocol, no clinician report. It measures your breath after meals you choose, which answers a different question from a standardised substrate challenge.
Going deeper on any of these
Breath test prep, and why the instructions disagreeEvery lab publishes its own prep rules and they do not match. A prep failure produces no error message, just a number that looks real.
Hydrogen sulfide testing: one test, no thresholdOne breath test on the US market measures hydrogen sulfide. No published guideline sets a threshold for what the number means. Both facts matter before you buy.
Lactulose or glucose? They rarely agreeThe two common breath tests use different sugars and reach different parts of the gut. Where patients took both, they rarely made the same diagnosis.
Reading a breath test resultWhat the published cutoffs are, where they came from, and which gas has no agreed threshold at all. A number is not a verdict.
Retesting, and what a second result actually tells youA second test is only a confirmation if it asks the same question. Change the substrate or the lab and you have a new measurement, not a check on the first.
Tests sold for this that do not measure itStool panels, food sensitivity panels and organic acid tests are sold for overgrowth questions. What each measures, and why that differs.
The DAO blood test: not conclusive, widely soldA national allergy guideline says serum diamine oxidase testing cannot be considered conclusive. It remains one of the most commonly sold tests in this space.
What makes a breath test wrong, in both directionsA positive can come from the colon rather than the small intestine. A negative can mean the gas was never measured. Both errors read as clean results.
Why there is no hydrogen sulfide threshold to compare against
The short answer
The North American Consensus sets thresholds for hydrogen and methane and contains no hydrogen sulfide criterion at all. So even a three gas test returns a number with no published cutoff behind it. Measuring something is not the same as knowing what counts as abnormal.That gap is why we describe the three gas test as answering a narrower question than it appears to. It tells you a value. The interpretation of that value rests on work that is still in progress, and the most honest version of this page says so rather than implying a clean cutoff exists.
What we relied on
- Pimentel M et al., American Journal of Gastroenterology 2020 Clinical guidelineNo single symptom can be specifically attributed to SIBO. All six recommendations are conditional, and five of the six rest on very low quality evidence.
- Rezaie A et al., American Journal of Gastroenterology 2017 Clinical guidelineA hydrogen rise of 20 ppm or more over baseline by 90 minutes is positive. Methane of 10 ppm or more at any point is positive. The consensus contains no hydrogen sulfide threshold.
- Scalese G et al., Journal of Clinical Medicine 2025 Peer-reviewed studyCross-sectional study of 564 outpatients. Clinical symptoms were not predictive of SIMO subtypes. In the subgroup of 47 patients who underwent both breath tests, 74.0% of overgrowth diagnoses were identified by lactulose alone and 13.0% by glucose alone; only 8.7% were concordant. The authors state the kappa concordance index could not be calculated because the subgroup was too small.
- Kashyap P et al., Neurogastroenterology & Motility 2024 Peer-reviewed studyBreath testing is inaccurate and should be abandoned. The methane and hydrogen sulfide criteria have never been validated.We have not yet confirmed a direct link to this document, so we are not giving you one. The citation is enough to find it, and we would rather say this than send you to a journal front page.
Common questions
- Which SIBO breath test measures hydrogen sulfide?
- Of the five tests we track, one measures hydrogen sulfide directly. The others detect hydrogen and methane only and physically cannot register the third gas, so a negative from one of them is not information about hydrogen sulfide.
- Is a more expensive breath test better?
- Only if the extra money buys a capability you need. The three gas test costs more because it measures an additional gas. If hydrogen sulfide is not part of your question, that capability is not worth the difference to you.
- What does a negative breath test actually rule out?
- Only the gases the test can measure, at the thresholds published for them. A two gas test returning negative leaves hydrogen sulfide entirely unexamined, and no breath test rules out the several other conditions that produce the same symptoms.
- Do I need a prescription?
- It depends on the test. Some are sold direct to consumers with no clinician involved, others are practitioner-ordered only. Both arrangements appear in the table above, and direct access also means nobody interprets the result for you.
- Is there an agreed threshold for hydrogen sulfide?
- No. The North American Consensus sets thresholds for hydrogen and methane and contains no hydrogen sulfide criterion at all. So even a three gas test returns a number with no published cutoff behind it, which is a real limitation rather than a technicality.