The Bloating Nobody Explained: How SIBO Is Tested and Why It Gets Missed

That normal result is not the end of the search. Small intestinal bacterial overgrowth, or SIBO, is one of the hardest common problems to test cleanly, and a single breath test measures only part of the picture. Healz is equipped with root-cause technology that keeps asking the questions one breath test cannot answer, so the cause behind the bloating gets found instead of renamed.

What SIBO Actually Is

The small intestine is meant to be relatively sparse of bacteria. Most of your gut flora lives in the colon, further downstream. SIBO is what happens when bacteria that belong lower in the tract set up in excess in the small intestine, where they ferment carbohydrates before your body finishes absorbing them.

That fermentation produces gas, and gas is the symptom you feel: bloating, distension, belching, cramping, and either loose stools or constipation. SIBO does not announce itself. It hides inside the same complaints that get labeled irritable bowel syndrome, and the two genuinely overlap, which is exactly why the label sticks before the cause is checked. If your workup stopped at a label, the pattern in It's Just IBS Is a Label, Not a Cause: The Root-Cause Workup Behind Irritable Bowel Syndrome is worth reading alongside this one.

How the Breath Test Works

You cannot easily sample the small intestine, so testing relies on an indirect signal. You drink a sugar, the bacteria that ferment it release hydrogen and methane, and some of that gas comes out in your breath, where a machine measures it in parts per million over two to three hours. Two things vary, and both matter.

Glucose versus lactulose. Glucose is absorbed high in the small intestine, so a glucose breath test mostly reads the proximal segment. It is more specific but can miss overgrowth further down. Lactulose is not absorbed, so it travels the whole small bowel and can catch distal overgrowth, but that reach makes it prone to false positives when normal colonic bacteria ferment it. The North American Consensus set the doses at 75 g for glucose and 10 g for lactulose to make results comparable.

Hydrogen versus methane. A rise in hydrogen of at least 20 ppm above baseline within 90 minutes is the consensus cutoff for a positive test. Methane is a separate story. Methane is not made by bacteria at all. It is produced by archaea, most often Methanobrevibacter smithii, and a methane level of at least 10 ppm at any point signals what is now called intestinal methanogen overgrowth, or IMO. That distinction is practical: methane tends to slow gut transit, so IMO shows up more often as constipation than as diarrhea, and it does not respond to the same treatment.

Why It Gets Missed

Here is the honest part the leaflet leaves out: the breath test is not a clean yes or no. Against the imperfect reference standard of fluid sampling from the small intestine, one pooled analysis put the glucose breath test near 54% sensitivity and the lactulose test near 42% (per Clinical Gastroenterology and Hepatology). Sensitivity in that range means a real case can easily produce a normal-looking result. And because small bowel aspiration has its own contamination problem, the true accuracy of breath testing cannot even be pinned down precisely, a limitation both the ACG guideline and a joint ANMS and ESNM practice update have stressed.

Several things throw the result off. Fast intestinal transit can push lactulose into the colon early and mimic overgrowth. Recent antibiotics, what you ate the day before, and how the baseline was measured all move the numbers, and a test run for too short a window can end before a distal rise appears.

Then there is the overlap that makes SIBO easy to bury. SIBO is more common in people who carry an IBS diagnosis, and a positive breath test actually predicts who is more likely to improve on the antibiotic rifaximin. A single 7 to 10 day course helps a large share of hydrogen-predominant SIBO, but methane-driven IMO is far more stubborn and usually needs combination therapy. So the same word, "SIBO," hides two different problems with two different treatments, and a test read in isolation can send someone down the wrong one.

The breath test is not useless. A normal number is a data point, not a verdict, and the symptoms deserve to be read as a pattern across your whole history rather than dismissed on one imperfect reading. That is the same discipline behind reading any lab result by trend and context instead of a single line, which we cover in Normal Describes a Population, Not You: Reading a Blood Test Beyond the Range.

How Healz Works

The problem with bloating is that it never sits with one specialist, and one test rarely settles it. Healz puts the whole case in one chat instead of ten apps, and inside that one place sits what actually moves a stuck diagnosis.

Frontier AI, the strongest AI, works your case directly. Healz is equipped with root-cause technology, which is why it treats a normal breath test as one clue rather than a stop sign: it asks whether glucose or lactulose was used, whether the window was long enough, whether methane was even measured, and cross-checks your symptom pattern against more than a million rare and complex cases to see what a single number missed. Its memory holds every result you upload, your breath test, your prior labs, your symptom timeline, and connects them over months so a shift no single visit would notice becomes visible. Drop in a breath test PDF or any lab report and the AI reads it in full context, an AI lab report reader that ties the finding back to the rest of your record. And when you want a human read on the plan, you can bring a board-certified doctor into the same chat for a second opinion.