SIBO Breath Test Guide: Preparation, Types, and How to Read Your Results

The SIBO breath test is the most widely used non-invasive method for diagnosing Small Intestinal Bacterial Overgrowth. While the test itself is straightforward, understanding how to prepare properly, which type of test to request, and how to interpret your results can significantly affect diagnostic accuracy. Missteps in preparation or interpretation lead to false results and delayed treatment.

This guide covers everything you need to know about SIBO breath testing, from the science behind how it works to practical tips for getting the most accurate results possible.

How Does the SIBO Breath Test Work?

The breath test relies on a simple principle: humans do not produce hydrogen or methane gas on their own. These gases are exclusively produced by microbial fermentation of carbohydrates. When you ingest a test substrate (either lactulose or glucose), any bacteria present in the small intestine will ferment it and produce gases that are absorbed into the bloodstream, travel to the lungs, and appear in your exhaled breath.

By collecting breath samples at regular intervals over 2 to 3 hours and measuring gas concentrations, the test can determine whether bacteria are fermenting the substrate in the small intestine (which would produce an early rise in gas levels) versus the large intestine (which would produce a later rise).

What Is the Difference Between Lactulose and Glucose Breath Tests?

The two main SIBO breath tests use different substrates, and each has distinct advantages and limitations.

The lactulose breath test uses lactulose, a synthetic sugar that humans cannot digest or absorb. Because it passes through the entire gastrointestinal tract unabsorbed, it can detect bacterial overgrowth anywhere in the small intestine, including the distal (far) end near the junction with the large intestine. However, because lactulose always reaches the colon and is fermented there, distinguishing between a late small intestinal rise and an early colonic rise can be challenging. This contributes to a higher false positive rate.

The glucose breath test uses glucose, which is rapidly absorbed in the upper small intestine. If bacteria are present in the proximal (near) small intestine, they will ferment the glucose before it is absorbed, producing a measurable gas rise. The advantage is high specificity, meaning fewer false positives. The disadvantage is that glucose is absorbed so quickly that it may never reach the distal small intestine, meaning overgrowth in that region can be missed, resulting in false negatives.

Most SIBO-literate practitioners prefer the lactulose breath test for its broader detection range, accepting the trade-off of potentially more false positives. Some practitioners order both tests for a more complete picture.

How Should I Prepare for a SIBO Breath Test?

Proper preparation is essential for accurate results. Inadequate preparation is one of the most common causes of misleading test outcomes.

One month before the test: Avoid antibiotics, including herbal antimicrobials, as they can temporarily reduce bacterial populations and cause false negatives. Discuss any current medications with your ordering provider.

One week before the test: Stop taking probiotics, as they can alter fermentation patterns and gas production. Also stop prokinetic agents, laxatives, and stool softeners, as these affect transit time.

One day before the test (preparation diet): Follow a strict low-residue, low-fermentation diet. The goal is to starve bacteria of their food so that any gas production during the test can be attributed to the test substrate rather than residual food.

Allowed foods on the preparation day include plain white rice, plain baked or broiled chicken, turkey, or fish, eggs prepared without dairy or oil, plain white bread (without garlic or onion), and small amounts of butter or olive oil. Salt is the only permitted seasoning. Avoid all fruits, vegetables, dairy, legumes, nuts, seeds, fiber supplements, sugar alcohols, and anything containing garlic or onion.

The night before the test: Eat your last meal by 7 PM or at least 12 hours before the test. After your last meal, you may drink only plain water.

The morning of the test: Do not eat, drink anything other than a small sip of water, smoke, exercise vigorously, or chew gum. Brush your teeth with a small amount of toothpaste and rinse thoroughly. These precautions prevent oral bacteria from contaminating your baseline breath sample.

How Do I Read My SIBO Breath Test Results?

Understanding your results requires knowing what the numbers mean and which diagnostic criteria your practitioner is using.

Baseline values: Your first breath sample, taken before drinking the test substrate, establishes your baseline. Ideally, baseline hydrogen should be below 10 parts per million (ppm) and baseline methane below 10 ppm. Elevated baseline values may indicate inadequate preparation or a very active overgrowth.

Hydrogen interpretation: According to the 2017 North American Consensus, a rise in hydrogen of 20 ppm or more above baseline within 90 minutes of ingesting the substrate is considered a positive result for hydrogen-dominant SIBO. The timing matters because a rise after 90 minutes more likely reflects colonic fermentation, particularly with lactulose.

Methane interpretation: A methane level of 10 ppm or more at any point during the test is considered positive for methane-dominant SIBO (also called Intestinal Methanogen Overgrowth or IMO). Unlike hydrogen, methane does not need to show a specific pattern of rise because methane production by archaea can occur throughout the intestine.

Hydrogen sulfide interpretation: Newer breath test technologies like the trio-smart test can measure hydrogen sulfide. Elevated hydrogen sulfide levels of 3 ppm or more at any point during the test suggest hydrogen sulfide SIBO. This is a newer diagnostic criterion and research is ongoing.

Flat-line results: If both hydrogen and methane remain flat and low throughout the test, this could mean you do not have SIBO, or it could indicate hydrogen sulfide SIBO (if that gas was not measured), or a false negative due to recent antibiotic use or inadequate preparation.

What Causes False Positive and False Negative Results?

No diagnostic test is perfect, and the breath test has known limitations that are important to understand.

Common causes of false positives include rapid intestinal transit, which moves the substrate into the colon early, producing a gas rise that mimics small intestinal overgrowth. Inadequate preparation that leaves fermentable residue in the gut can elevate baseline values and create confusing patterns. Some oral bacteria can produce hydrogen if the mouth is not clean before testing.

Common causes of false negatives include recent use of antibiotics or antimicrobials that have temporarily reduced bacterial counts. Using glucose as the substrate can miss distal SIBO. Slow transit time can delay the gas rise, making it fall outside the diagnostic window. Testing only for hydrogen and methane will miss hydrogen sulfide SIBO.

If your test results do not match your clinical picture, discuss retesting or alternative testing approaches with your provider. Some practitioners choose to treat empirically based on symptoms when clinical suspicion is high despite a negative test. For more on how SIBO and IBS symptoms overlap, see our guide on the connection between SIBO and IBS.

What Do the Different Gas Types Mean for Treatment?

Your gas pattern directly influences your treatment approach and dietary strategy.

Hydrogen-dominant SIBO typically responds well to rifaximin alone or herbal antimicrobials. The dietary approach for hydrogen SIBO focuses on reducing rapidly fermentable carbohydrates. Diarrhea is the most common bowel pattern.

Methane-dominant SIBO (IMO) usually requires combination therapy, such as rifaximin plus neomycin or rifaximin plus metronidazole. The dietary approach for methane SIBO involves careful fiber management and attention to constipation. Methane directly slows gut transit, creating a self-perpetuating cycle.

Hydrogen sulfide SIBO is the least well-understood type and treatment protocols are still being refined. Bismuth-based treatments and low-sulfur diets may be beneficial. Restricting sulfur-containing foods like eggs, cruciferous vegetables, and alliums is often recommended.

FODMAPSnap’s SIBO profile feature allows you to specify your bacteria type, whether hydrogen, methane, or hydrogen sulfide, and your current treatment phase, so the app tailors its meal analysis and food recommendations to your specific situation.

How Often Should I Retest?

Retesting is an important part of SIBO management. Most practitioners recommend retesting 2 to 4 weeks after completing an antimicrobial course to assess whether treatment was successful. Follow the same preparation protocol as your initial test for comparable results.

If your retest shows improvement but not full resolution, your provider may recommend an additional round of treatment. If results are negative but symptoms persist, other conditions may be contributing, and further investigation is warranted. The IBS and SIBO education hub covers the broader diagnostic landscape.

Ongoing monitoring is also valuable for patients with a history of SIBO relapse. Some practitioners recommend periodic retesting every 6 to 12 months, especially if symptoms begin to recur.

For a comprehensive overview of SIBO, including treatment phases and dietary management, see our SIBO guide and SIBO diet plan.

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This article is for informational purposes only and does not constitute medical advice. SIBO breath test results should be interpreted by a qualified healthcare provider in conjunction with your clinical history and symptoms. Do not self-diagnose or self-treat based on test results alone.