SIBO Breath Tests

In short: a SIBO breath test measures the hydrogen and methane (and, with newer tests, hydrogen sulfide) that gut microbes make after you drink a sugar solution. By the North American consensus, a hydrogen rise of 20 ppmParts per million (ppm) The unit breath-test laboratories use to report the concentration of hydrogen, methane and hydrogen sulfide in a breath sample. or more within 90 minutes suggests SIBO, and methane of 10 ppm or more at any point suggests intestinal methanogen overgrowthIntestinal methanogen overgrowth (IMO) Overgrowth of methane-producing archaea, mainly Methanobrevibacter smithii. It is diagnosed by a breath methane level of 10 ppm or more and is linked to constipation. (IMO)¹. The test is non-invasive and cheap, but it is indirect: compared with culture of intestinal fluid, the glucose test detects only about half of cases, and the lactuloseLactulose A synthetic sugar the body cannot digest or absorb. As a breath-test substrate it travels the whole small intestine, which also makes false positives more likely. test is less reliable still⁴.

Small intestinal bacterial overgrowth (SIBO) can be diagnosed directly by culturing fluid taken from the small intestine during an endoscopy, but that is invasive and expensive. Breath tests are the practical alternative and are endorsed by both the US and European guidelines, with caveats³². Methane overgrowth can only be diagnosed by breath testing in routine practice⁵.

What the test measures

Hydrogen and methane are made only by microbes in the gut, not by human cells. When microbes ferment the test sugar, these gases pass into the blood and are breathed out⁴.

• Hydrogen is made by bacteria. An early rise suggests bacteria are fermenting the sugar in the small intestine.
• Methane is made by archaeaArchaea Single-celled microorganisms that are distinct from bacteria. Methane-producing archaea (methanogens) are responsible for intestinal methanogen overgrowth., mainly Methanobrevibacter smithii, from the hydrogen that bacteria release. Methane slows the gut: in a 2006 animal study it slowed small-intestinal transit by 59%¹¹. High levels are called intestinal methanogen overgrowth (IMO) rather than SIBO.
• Hydrogen sulfide is made by sulfate-reducing bacteriaSulfate-reducing bacteria Bacteria such as Desulfovibrio that consume hydrogen and sulfur compounds and produce hydrogen sulfide gas.. Most breath analyzers in clinical use cannot measure it⁴, but newer three-gas tests can. In a 2022 study of people with IBS, higher breath hydrogen sulfide went with more sulfide-producing bacteria in stool and with diarrhea⁹. See our guide to hydrogen sulfide SIBO.

Measuring hydrogen and methane together is now the recommended standard, and measuring carbon dioxide alongside them helps laboratories spot poor-quality samples⁴.

Glucose or lactulose?

The sugar you drink determines which part of the small intestine is tested.

• Glucose is absorbed in the upper small intestine, so it rarely reaches the colon. It produces fewer false positives but can miss overgrowth further down.
• Lactulose is a synthetic sugar the body cannot absorb, so it travels the whole small intestine. It can detect overgrowth anywhere, but it always reaches the colon, and if it gets there quickly, normal colonic bacteria produce a rise that looks like SIBO.

The sensitivity and specificity figures are pooled results from studies that compared breath tests with culture of jejunal fluid: 14 studies with 668 people for glucose and 4 studies with 214 people for lactulose⁴. The European guideline recommends glucose for people who have not had gut surgery, because its false-positive rate is lower².

Dose matters too. In a 2022 analysis of 725 breath tests, 10 g of lactulose gave fewer positive SIBO results than 16 g (42% vs. 53%), and 75 g of glucose gave more positive results than 50 g (36% vs. 22%)⁶.

How to prepare

The North American consensus and European guideline agree on most preparation steps¹²:

• Antibiotics: wait at least 4 weeks after finishing a course.
• Colonoscopy or bowel prep: wait at least 2 weeks (Europe).
• ProkineticsProkinetic A medication or supplement that stimulates gut movement. Prokinetics are often used after SIBO treatment to support the migrating motor complex and reduce relapse. and laxatives: stop at least 1 week before, if you can (North America).
• The day before: avoid fermentable foods such as complex carbohydrates and high-fiber foods. Plain meat, fish, eggs and white rice are typical choices.
• Fasting: 8 to 12 hours, with water only.
• On the day: no smoking, and avoid exercise or anything that makes you breathe hard, before and during the test.
• Mouth rinse: the European guideline recommends rinsing with an antiseptic such as chlorhexidine just before the first sample, to stop mouth bacteria fermenting the sugar².

There is no consensus on whether to stop probiotics before the test¹, and acid-reducing medicines (PPIsProton pump inhibitor (PPI) A class of acid-reducing medication used for reflux, such as omeprazole. Long-term use lowers stomach acid and is associated with a higher risk of SIBO.) do not need to be stopped¹.

The test itself

You give a baseline breath sample, drink the sugar dissolved in water, and then give a sample about every 15 minutes. The European guideline recommends 2 hours for a glucose test²; lactulose tests often run longer. You cannot eat until the test is over. Many people do the test at home with a kit, breathing into a bag and transferring the air into sealed tubes that are posted to a laboratory.

Reading the results

The main cut-offs¹³:

The European guideline stresses that the diagnostic criteria for SIBO “have not been confirmed and uniformly accepted”, and that a positive result should be weighed against how likely SIBO was before the test². To compare your own readings with these thresholds and see them as a graph, use our breath test interpreter.

Common patterns

• Double peak. An early hydrogen rise followed by a second, colonic rise was once thought to be typical of SIBO. The North American consensus concluded that a double peak is not required and should not be used to diagnose SIBO¹.
• High baseline. A high first reading can mean the preparation diet or fast was not followed, poor oral hygiene, or slow movement in the upper gut. Many centers treat the result as indeterminate and repeat the test⁴.
• Flat line. Little or no hydrogen or methane throughout is read as negative by standard criteria⁴. Researchers now regard it as a distinct pattern⁵, and one proposed explanation is that hydrogen sulfide producers are using up the hydrogen; only a three-gas test can check this. In addition, around 10% of people have gut bacteria that make too little hydrogen to detect².

How accurate are breath tests?

Breath tests measure gas, not bacteria, so several things can distort them²:

• Fast transit. If the sugar reaches the colon early, colonic fermentation looks like SIBO. In a 2011 study that tracked a lactulose test meal with imaging in 40 people with IBS, 5% or more of the meal had already reached the colon when hydrogen rose in 22 of 25 positive tests⁷.
• Slow transit. If the sugar moves slowly, a rise may come after the 90-minute cut-off and be missed.
• Substrate choice. A 2020 meta-analysis found that lactulose tests diagnosed SIBO 3.6 times more often than glucose tests in people with IBS, and 7.6 times more often in healthy controls⁸.

The European guideline notes that combining the breath test with an independent measurement of transit time, such as scintigraphy, reduces false results, but this is rarely available². In practice, results should be interpreted together with your symptoms and risk factors.

Common questions

Can I do a SIBO breath test at home?

Yes. Many laboratories send kits for home use; you collect the samples at set times and post them back. Follow the preparation steps carefully, because most invalid results come from diet, fasting or timing errors.

Can lactose or fructose tests detect SIBO?

Sometimes, but not reliably. In a 2024 study that compared tests done in the same 67 adults within 6 weeks, lactose breath tests agreed well with SIBO tests, but fructose tests gave false positives for SIBO in 27% of cases and missed 27% of methane overgrowth¹². Lactose tests are mainly used for lactose intolerance.

Should I retest after treatment?

Breath tests are often repeated after treatment to check whether the overgrowth has cleared, especially before deciding on another round¹. See our guides to antibiotics and herbal antimicrobials.