Which breath tests measure hydrogen sulfide?

Of the five we track, one does. The rest measure hydrogen and methane only and physically cannot register the third gas, so a negative result from one of them contains no information about hydrogen sulfide at all.

Is there a threshold for a positive hydrogen sulfide result?

Not in any published guideline. The North American Consensus sets criteria for hydrogen and methane and contains no hydrogen sulfide criterion. So a three gas test returns a number against a cutoff that no consensus body has established.

Then is the three gas test worth the extra money?

Only if hydrogen sulfide is genuinely part of your question. It buys you a measurement that a two gas test cannot make. It does not buy you an agreed interpretation of that measurement, and being clear about which of those you are paying for is the point of this page.

Can a test infer hydrogen sulfide without measuring it?

One provider infers it from a flat hydrogen curve. That is an inference rather than a measurement and it has not been validated against direct measurement, so we describe it as what it is rather than as a third gas result.

What are the reported symptoms?

In the largest case series available, a preprint drawing on a practitioner-sourced sample, bloating appeared in 77%, constipation in 50.8%, diarrhea in 42.6% and sulfur burps in only 10%. Sulfur burps are widely described as the signature sign and were the least common finding in that series.

Hydrogen sulfide testing

By B. Gray Randolph · Updated August 5, 2026

This is the single most expensive piece of missing information in the whole category, and it is not complicated.

The two facts that matter

One breath test on the US market measures hydrogen sulfide directly. No published guideline sets a threshold for what the resulting number means. Both of those are true at once, which means the test can tell you a value that nobody has agreed how to interpret. Knowing that before you pay is the difference between buying a measurement and buying an answer.

Test	Hydrogen	Methane	Hydrogen sulfide	Price	Prescription
trio-smartGemelli Biotech	Yes	Yes	Yes	$349–369verified 2026-08-03	No
SIBO 2-hour / 3-hourGenova Diagnostics	Yes	Yes	No	$225–349verified 2026-08-03	Yes
SIBO breath testCommonwealth Diagnostics International	Yes	Yes	No	$295verified 2026-08-03	Yes
QuinTron breath testQuinTron / breathtests.com	Yes	Yes	No	$195–249verified 2026-08-03	No
SIBO breath testAerodiagnostics	Yes	Yes	No	$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: 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: 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: 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: 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: 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.

Why a negative from the wrong test is not a negative

A two gas test cannot detect hydrogen sulfide. Not poorly, not unreliably: it has no sensor for it. So a negative result from one leaves that gas entirely unexamined, and treating it as a rule-out is reading an answer into a question that was never asked. Unmeasured and absent are different things.

This is the specific sequence that costs people money and time. Someone suspects overgrowth, buys the cheaper test on the reasonable assumption that a SIBO test tests for SIBO, gets a negative, and stops. Nothing on the packaging tells them which gases were in scope.

The missing threshold

Rezaie A et al., American Journal of Gastroenterology 2017 Clinical guideline

That consensus sets a hydrogen criterion and a methane criterion. It contains no hydrogen sulfide criterion at all. So even with a direct measurement in hand, the question of what counts as high is unsettled at the level of the field, not just at the level of your clinician.

What is not settled here

We think this is the most honest framing available: the three gas test answers a question the two gas test cannot, and the interpretation of that answer is still being worked out. Sites presenting a clean cutoff are ahead of the published evidence. So is any site telling you the measurement is worthless.

What the symptom picture actually looks like

Goldenberg J et al., medRxiv 2023 Preprint, not peer reviewedWe have not yet confirmed a direct link to this document, so we are not giving you one. The citation above is enough to find it, and we would rather say this than send you to a journal front page.A preprint drawing on a practitioner-sourced convenience sample. Not peer reviewed, and the sample is self-selected by clinicians who were already looking for hydrogen sulfide.

Worth reading carefully, and worth noting what it does to a widely repeated claim. Sulfur burps are commonly described as the signature sign of hydrogen sulfide overgrowth. In that series they appeared in 10% of confirmed cases, making them one of the least common findings rather than a hallmark.

That is also why we do not offer a symptom questionnaire that predicts your gas. The published profiles for methane and hydrogen sulfide are close to identical, and around a quarter of cases in that series were positive for both, so a tool that returns a single answer is wrong by construction for a substantial share of users.

What to do with this

Decide whether hydrogen sulfide is genuinely part of your question before you choose a test, because that decision is what selects the test rather than the other way around. Then take the result, whatever it is, to a clinician who can put it next to everything else about you.

Common questions

Which breath tests measure hydrogen sulfide?: Of the five we track, one does. The rest measure hydrogen and methane only and physically cannot register the third gas, so a negative result from one of them contains no information about hydrogen sulfide at all.
Is there a threshold for a positive hydrogen sulfide result?: Not in any published guideline. The North American Consensus sets criteria for hydrogen and methane and contains no hydrogen sulfide criterion. So a three gas test returns a number against a cutoff that no consensus body has established.
Then is the three gas test worth the extra money?: Only if hydrogen sulfide is genuinely part of your question. It buys you a measurement that a two gas test cannot make. It does not buy you an agreed interpretation of that measurement, and being clear about which of those you are paying for is the point of this page.
Can a test infer hydrogen sulfide without measuring it?: One provider infers it from a flat hydrogen curve. That is an inference rather than a measurement and it has not been validated against direct measurement, so we describe it as what it is rather than as a third gas result.
What are the reported symptoms?: In the largest case series available, a preprint drawing on a practitioner-sourced sample, bloating appeared in 77%, constipation in 50.8%, diarrhea in 42.6% and sulfur burps in only 10%. Sulfur burps are widely described as the signature sign and were the least common finding in that series.