Does Your SIBO Breath Test Result Depend on the Lab? What a New Study Found
A 2026 study found the same SIBO breath sample can read positive or negative depending on the cutoff your lab uses. What that means for your result.
Image by Myriams-Fotos via Pixabay
Does Your SIBO Breath Test Result Depend on the Lab? What a New Study Found
Here is something most patients never hear: the same breath sample can be called positive at one lab and negative at another, because labs do not all draw the diagnostic line in the same place. A 2026 study put two of the common cutoffs side by side and found that the lower one diagnosed more cases of SIBO, and that it was the one that actually tracked who felt worst. It does not change how SIBO gets treated. It does change how you should read your own report.
SIBO, or small intestinal bacterial overgrowth, is when bacteria that belong lower in your gut start setting up shop in the small intestine, where they ferment your food too early and produce gas. That gas is what a breath test is trying to catch. If you want the broader picture of how SIBO is diagnosed and managed, the SIBO and motility hub is a good place to start. This post is about one narrow, surprisingly large detail: the line drawn on the result.
What the study actually found
Researchers in Kuala Lumpur followed 90 adults with irritable bowel syndrome and gave each of them a glucose hydrogen breath test, the kind where you drink a sugar solution and your breath is sampled over the next few hours to see how much gas your gut bacteria produce. Then they scored every result two ways.
Under the Asia-Pacific consensus cutoff, where a hydrogen rise of at least 12 parts per million above your starting breath counts as positive, 44.4% of the group came back positive for SIBO. Under the North American consensus cutoff of at least 20 parts per million, only 37.8% did. Same people, same breaths, two different answers for roughly one in fifteen patients. Methane of at least 10 parts per million counted as positive under both, so the disagreement was entirely about where the hydrogen line sat.
The part that gives the finding weight is what happened next. Only the lower, Asia-Pacific cutoff lined up significantly with how severe people's symptoms were. The stricter North American line missed some of the patients who were, by their own scores, the most miserable.
So what is a "cutoff," anyway?
A breath test does not return a simple yes or no. It returns a curve: how much your breath hydrogen climbs, in parts per million, after you drink the sugar. Somebody has to decide how big that climb has to be before we call it SIBO. That decision is the cutoff.
The North American consensus, published in 2017, set its line at a rise of 20 parts per million within 90 minutes. The Asian-Pacific consensus drew it lower. Neither number fell out of the sky. They are expert judgment calls about where "enough gas to matter" begins, and reasonable experts landed in different places. So when your report says "negative," it means negative by the line this particular lab chose to use.
What the study does not claim
This is one study, and a modest one. It was a single center, 90 people, all of whom already had IBS, and it used the glucose substrate only. The authors are careful to frame their recommendation for the lower cutoff as population-specific, suggested particularly for Asian populations, rather than a new global rule. International guidelines are not changing on the strength of one paper.
So this is not a green light to assume every negative result you have ever had was wrong, nor a reason to march off and re-test for its own sake. It is a well-designed reminder that the line is movable, and that the stricter line can miss real cases.
How I read this in clinic
This rhymes with something I have been telling patients for a long time. A "negative" breath test is not always a no. Usually I'm talking about the gases a test skips. Most standard panels measure hydrogen and methane but leave out a third gas, hydrogen sulfide, so a low hydrogen result can hide an overgrowth that simply produces a different gas. (For the methane side of that picture, I dug into methane SIBO, also called IMO separately.)
What this study adds is a second example of the same lesson, using the one gas everybody already measures. Even for hydrogen, the line that decides positive from negative is not universal, and the stricter version of it overlooked the people who felt the worst.
In my practice, a borderline-negative breath test in someone whose symptoms clearly fit SIBO is one of the most common reasons a real problem gets waved off. The number came back just under the line, so the door closed, and nobody asked which line was being used. I wrote separately about whether the SIBO breath test is reliable enough to begin with; this is the narrower cousin of that question. Given how much rides on a single threshold, the result deserves to be read next to the person, not in place of them.
What to actually do with your result
You do not need to become a breath-test expert. You do need a few questions in your pocket.
- Ask which substrate and which criteria your lab used. Glucose and lactulose breath tests behave differently, and the positive cutoff can differ too. It is usually on the report, and if it is not, the lab can tell you.
- Put the number next to your symptoms. A borderline-negative result alongside a symptom picture that clearly fits SIBO is a reason to keep looking, not a reason to stop.
- Bring it to a provider who reads both. The goal is not more testing for its own sake. It is a conversation that weighs the gas number, the substrate, your history, and how you actually feel, all together.
The gas number is only as fixed as the line your lab drew under it. How you feel, and the rest of your history, are what tell you whether that line landed in the right place. The number on the page is the easiest thing to over-trust, and Loh's study shows why: the stricter cutoff missed the people who felt the worst.
Reading your own breath-test report critically is one piece of a larger SIBO plan. If you want to see how testing, treatment phases, and motility fit together, the SIBO Treatment Algorithm walks through it step by step.
FAQ
Can the same SIBO breath test be positive at one lab and negative at another?
Yes. If two labs apply different diagnostic cutoffs to the same breath sample, one can call it positive while the other calls it negative. The 2026 study showed exactly this: the lower hydrogen cutoff flagged 44.4% of patients and the higher one flagged 37.8%, from the same breaths.
What is the difference between the Asia-Pacific and North American SIBO cutoffs?
They draw the positive line at different gas levels. The North American consensus calls a glucose hydrogen breath test positive when hydrogen rises at least 20 parts per million above baseline. The Asia-Pacific consensus uses a lower line, a rise of at least 12 parts per million. The lower line labels more people positive.
Does a lower cutoff just mean more false positives?
Not necessarily. A lower line does catch more people, which can include some who would not have symptoms. But in this study the lower cutoff was the one that lined up with how severe people's symptoms actually were, which suggests it was catching real cases the stricter line was missing.
Should I get retested if my result was borderline negative?
Not automatically. A borderline-negative result in someone whose symptoms fit SIBO is worth a conversation with your provider, not a reflex re-test. Bring the report, the substrate used, and your symptom history, and decide together whether anything should change.
Does this study change how SIBO is treated?
No. It does not introduce a new treatment or overturn an existing one. What it changes is interpretation: it is a reminder that the number on your report depends on which line the lab drew, so the result should be read alongside your symptoms rather than as a standalone verdict.
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