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Faculty from Division of Gastroenterology, Hepatology and Nutrition Publish Research on Hydrogen-Methane Breath Testing for Small Intestinal Bacterial Overgrowth

July 21, 2023

Hydrogen-methane breath testing is an inexpensive and noninvasive alternative to diagnose small intestinal bacterial overgrowth (SIBO), which can cause gastrointestinal symptoms like diarrhea, bloating, and abdominal pain.

Yet, direct culture of small intestinal contents, a more costly and invasive test that requires an endoscopy, remains the gold standard to diagnose SIBO. Additional limitations include lack of standardized techniques and tools for aseptic collection of contents and contamination of samples from oral bacteria.  

David Levinthal, MD, PhD, and Aylin Tansel, MD, MPH, both experts from the UPMC Digestive Health Care and University of Pittsburgh Division of Gastroenterology, Hepatology and Nutrition, recently published research on hydrogen-methane breath testing in Clinical and Translational Gastroenterology. When used appropriately, breath testing can greatly aid in the diagnosis of SIBO. In their article, “Understanding Our Tests: Hydrogen-Methane Breath Testing to Diagnose Small Intestine Bacterial Overgrowth,” Dr. Tansel and Dr. Levinthal provide an overview of breath testing that includes:

  • Indications for testing
  • The test paradigm
  • How the test is performed
  • Strategies to optimize test performance
  • Result interpretation
  • Complementary and alternative tests
  • How breath testing should be used in research and clinical care settings
  • Billing and cost information

Factors to Consider Before Test Administration

Common symptoms of SIBO include diarrhea, bloating, weight loss, abdominal pain, and constipation. Presenting symptoms can be considered when deciding to administer a breath test, in addition to patient demographics and choice of test substrate. 

Hydrogen-methane breath testing involves administering a carbohydrate substrate, typically either glucose or lactulose, which then produce gases via fermentation by gut bacteria. These gases, which include hydrogen, methane, and hydrogen sulfide gases, are absorbed from the gut into the blood circulation and then measured via exhalation from the lungs using commercially available gas analyzers. The test offers flexibility for patients as it may be performed in the office or even at home.

To ensure accurate breath testing results, it’s critical for patients to follow certain protocols before the test to avoid factors that may influence gas production. For example, Dr. Tansel and Dr. Levinthal outline a low-residue diet that should be followed the day before the test. If dietary preparation isn’t followed, high levels of gases may already be present before the test and could skew results.

In addition, use of laxatives, promotility drugs, opioids, and antibiotics should be avoided for certain time periods, if tolerable, prior to the test. “Each of these medications have their own unique effect on intestinal transit time, which can then impact the interpretation of the breath test,” Dr. Tansel says.

Opioids, for example, delay intestinal transit time, and should be stopped at least 24 hours before a breath test is administered. Antibiotics, on the other hand, reduce bacterial loads in the gut and therefore can alter the composition of hydrogen and methane in exhaled breath considerably. If possible, antibiotics should be stopped about a month before the test. 

Additional preparatory factors to consider before the test include cessation of smoking the night before the test and throughout the testing period, as well as minimizing physical exercise, as both have been shown to alter results.

“Various factors and conditions can influence results that should be taken into account before administering the test,” Dr. Levinthal says. “For example, some studies advocate for the use of chlorhexidine mouthwash before administering the substrate to eliminate fermentation from bacteria in the mouth, yet more research is needed.”

Administering and Interpreting a Breath Test

The first step for breath test administration is collecting a baseline sample followed by ingestion of the chosen substrate. After the substrate is consumed, samples of exhaled breath are then collected in regular intervals (generally every 15 or 20 minutes) over the course of about 180 minutes. Patients can breathe normally into the gas analyzer, and gas samples are immediately sent for analysis after collection.

Gas levels in the breath are measured in parts per million (ppm), and current guidelines state that a reading of hydrogen gas rise of ≥20 ppm from baseline by 90 minutes, and a methane gas rise of ≥10 ppm at any time during the study period constitute a positive breath test for SIBO. This standard is used in both clinical and research settings.

Metrics of test performance characteristics suggest that breath testing is a moderately good test to diagnose SIBO. However, hydrogen-methane breath testing alone may not be best for every patient care scenario, and there are several other complementary and alternative tests available.

Patients with Roux-en-Y gastric bypass (RYGB), for example, often have highly variable orocecal transit time (OCTT), so the 90-minute cutoff period from baseline for hydrogen gas rise may not be a reliable measure for this patient population. This suggests that measuring OCTT in addition to administering the breath test would be beneficial to diagnose SIBO in individuals with RYGB. However, given that measuring OCTT is invasive and is not well defined in this patient population, in addition to the fact that the prevalence of SIBO in RYGB patients is quite high, empiric antibiotic treatment may be best.

Breath testing is noninvasive and safe to perform, according to Dr. Tansel and Dr. Levinthal, and more research could improve its clinical utility and diagnostic accuracy.

“Further research could help define ideal treatment protocols, technique, and interpretation of results,” Dr. Tansel says. “Also, it would be beneficial to develop certain nuances such as a strongly positive versus moderately positive result, instead of just positive versus negative.”

Read more in Clinical and Translational Gastroenterology. Visit UPMC Physician Resources for more information.