Introduction
Abdominal bloating, abdominal distension, excessive gas, abdominal pain, and altered bowel habits are common reasons for referral to gastroenterology clinics. These symptoms are nonspecific, and may reflect disorders of gut–brain interaction, carbohydrate malabsorption or intolerance, small intestinal bacterial overgrowth (SIBO), intestinal methanogen overgrowth (IMO), motility disorders, altered gastrointestinal anatomy, pancreatic exocrine insufficiency, celiac disease, inflammatory bowel disease, or other conditions.
Hydrogen and methane are produced by microbial metabolism in the intestinal lumen and are not generated by human cells. After production in the gut, these gases are absorbed into the bloodstream and exhaled [1,2]. This physiologic principle supports the use of breath testing as an indirect measure of carbohydrate fermentation and microbial overgrowth [2-4]. In carbohydrate malabsorption, unabsorbed sugars reach the colon and are fermented by bacteria and methanogens. In SIBO or IMO, a significant early rise in hydrogen or methane may occur because fermentation takes place in the small intestine [2,3,5].
Methanogens are archaea rather than bacteria. Methanobrevibacter smithii is the predominant methanogen identified in many methane-positive patients [6]. The term IMO is increasingly preferred when methane production is the key abnormality, because methanogens can inhabit both the small and large intestine [5,7]. Methane production is clinically relevant because methane is associated with constipation and slower intestinal transit, and because conversion of hydrogen to methane can reduce hydrogen concentrations and thereby produce false-negative hydrogen-only tests [5,6,8,9].
Although breath tests are safe, simple, and widely available, their diagnostic performance is imperfect [3,10,11]. Test results are influenced by patient preparation, recent medications, antimicrobial exposure, substrate choice, baseline gas concentrations, sampling interval, reporting of symptoms, and orocecal transit time [2-4,11]. A rapid transit time can mimic an early rise after lactulose and therefore create a false-positive interpretation for SIBO [12-16], whereas methane production and altered anatomy can reduce sensitivity in other settings [8,17,18]. The absence of uniform local standards has resulted in inconsistencies among centers that perform breath testing.
The aim of this consensus guideline is to provide practical, standardized recommendations for indications, patient preparation, performance, interpretation and reporting of hydrogen- and methane-based breath tests in adult and pediatric patients with suspected SIBO, IMO, or carbohydrate malabsorption/intolerance.
Scope and target users
This document addresses breath testing for SIBO, IMO, and malabsorption or intolerance of lactose, fructose, sorbitol, and related fermentable carbohydrates. The recommendations are intended for gastroenterologists, pediatric gastroenterologists, neurogastroenterologists, dietitians, laboratory directors, technicians, and referring physicians who request or interpret breath tests.
This document does not replace clinical judgment. Results should be interpreted in the context of the individual patient, including pretest probability, alarm features, previous gastrointestinal surgery, medication exposure, underlying motility disorders, and alternative diagnoses.
Consensus development process
At the recommendation of the Israeli Gastroenterology Association, a panel was convened that included experts in adult and pediatric neurogastroenterology, clinical nutrition and dietetics, and directors of gastroenterology laboratories. The panel members had extensive experience in performing and interpreting breath tests, and in managing patients with suspected SIBO, IMO and carbohydrate intolerance.
Eight multidisciplinary meetings were held between February 2021 and February 2023. Before each meeting, the relevant literature and international guidance were reviewed. The panel discussed 5 core domains: indications for breath testing; pretest preparation and patient instructions; technical performance of breath tests; structured symptom questionnaires before and during testing; and interpretation and reporting of test results. Final statements were based on available evidence, international guidance, and expert consensus when evidence was limited.
Indications for breath testing
The panel supports breath testing in 4 main clinical scenarios (Table 1).
Table 1 Indications for breath testing
Direct diagnosis of SIBO by duodenal or jejunal aspirate culture or sequencing is invasive, expensive, susceptible to contamination, and rarely used in routine practice [2,10]. Breath testing is therefore the most practical diagnostic tool in most clinical settings [2,3,5,7]. Because symptoms overlap substantially with irritable bowel syndrome and other disorders of gut–brain interaction, objective testing can support clinical decision-making and improve physician-patient communication.
For suspected carbohydrate intolerance, 2 approaches are commonly used: supervised empirical dietary elimination or objective breath testing. The panel recognizes both approaches. However, when the response to dietary elimination is incomplete, ambiguous or difficult to interpret, objective testing is preferred. When SIBO is suspected, a dedicated SIBO/IMO breath test should generally precede carbohydrate testing, because SIBO can cause false-positive carbohydrate breath tests [19,20].
Patient preparation
Pretest preparation is essential, because recent antibiotics, probiotics, prebiotics, laxatives, prokinetics, bowel cleansing, diet, smoking, oral bacterial fermentation and exercise can alter baseline gas concentrations or transit time [2-4,11]. The goal is to minimize avoidable false-positive and false-negative results and to reduce test cancellations due to high baseline hydrogen.
Recommendations for patient preparation are summarized in Table 2.
Table 2 Patient preparation before breath testing
Technical performance of breath tests
Breath testing requires serial measurement of exhaled hydrogen and methane before and after ingestion of a test substrate. Results should be interpreted by the change from baseline, with attention to the timing of the rise and the symptoms reported during the test [2,3]. The panel recommends that laboratories use devices that measure hydrogen and methane simultaneously [2,3,5]. This approach improves the ability to identify IMO and methane producers, and reduces false-negative interpretation of hydrogen-only tests [8].
Symptoms should be recorded at baseline and at fixed intervals during the test [3,20]. Typical symptoms include bloating, distension, excessive gas, abdominal pain, diarrhea, constipation, and postprandial fullness. The report should indicate whether symptoms occurred during the test and whether they were typical of the patient’s usual complaints. Recommended substrates, sampling duration and pediatric doses are summarized in Table 3.
Table 3 Technical performance of breath tests and pediatric dosing
Choice of substrate for SIBO/IMO testing
Lactulose and glucose each have advantages and limitations. Lactulose is not absorbed in the small bowel and can detect fermentation along a larger length of intestine; however, early colonic arrival due to rapid orocecal transit may create false-positive results [3,12-16]. Glucose is absorbed in the proximal small bowel and may be more specific, but it may miss distal overgrowth because the substrate is absorbed before reaching the affected segment [3,10].
After considering these advantages and limitations, the panel recommends lactulose as the preferred substrate for SIBO/IMO testing, with glucose as an acceptable alternative. The report should state which substrate was used and should interpret positive results in light of pretest probability and potential transit confounding [3].
Baseline gas concentrations
A low baseline hydrogen concentration is desirable. High baseline hydrogen may reflect inadequate preparation, recent intake of fermentable carbohydrates, oral fermentation, or SIBO. The panel recommends attempting to lower an elevated baseline by asking the patient to rinse the mouth and drink water, followed by repeat baseline sampling. When baseline values remain above the recommended threshold, test cancellation and rescheduling should be considered. The approach to baseline gas concentrations is included in Table 4.
Table 4 Baseline gas concentrations and interpretation of breath test results