From the Research
A SIBO breath test is interpreted by analyzing the hydrogen and methane gas levels in a patient's breath over time after consuming a sugar solution, with a positive test typically showing an early rise in hydrogen levels (>20 ppm) or methane levels (>10 ppm) within 90 minutes of ingesting the test substrate, indicating bacterial overgrowth in the small intestine. The test usually involves collecting breath samples every 15-30 minutes for 2-3 hours after drinking a solution containing lactulose, glucose, or fructose. Different laboratories may use slightly different cutoff values, but generally, a rise of hydrogen by 20 ppm or more above baseline within the first 90 minutes suggests SIBO, as supported by the North American Consensus guidelines 1. For methane-producing organisms, a baseline methane level ≥10 ppm or a rise of ≥10 ppm during the test is considered positive, as noted in a study on lactulose breath testing 2. Some clinicians also look for a double peak pattern with lactulose testing, representing bacterial fermentation first in the small intestine and later in the colon.
Key points to consider when interpreting SIBO breath test results include:
- A rise in hydrogen of ≥20 ppm from baseline within 90 minutes suggests SIBO 1
- A baseline methane level ≥10 ppm or a rise of ≥10 ppm during the test is considered positive for methane-producing organisms 2
- False positives can occur with rapid transit time, while false negatives may happen with antibiotic use before testing, so patients should avoid antibiotics for 2-4 weeks before the test and follow a specific preparation diet for 24-48 hours beforehand that restricts fermentable foods
- Recent studies have demonstrated the expanding clinical utility of breath testing in the diagnosis, management, and prediction of treatment response in SIBO and particularly in IMO along with the identification of distinct breath test patterns such as flat-line and high baseline hydrogen 3
It's also important to note that breath testing has inherent strengths and limitations, and results must be interpreted with consideration of the clinical context and influencing factors, as discussed in a review of the pros and cons of breath testing for SIBO and IMO 3. Additionally, the diagnostic value of hydrogen sulfide breath testing has been evaluated, with a rise in H2S of ≥25.0 ppb or H2S levels ≥62.5 ppb at 90 min during lactulose breath test considered positive for SIBO, especially in constipation-predominant patients 4. However, the most recent and highest quality study on this topic is the 2021 study on the pattern of methane levels with lactulose breath testing, which suggests that the lactulose breath test for hydrogen and methane can be complete at 90 minutes 2.