Introduction

Small intestinal bacterial overgrowth (SIBO) is a commonly diagnosed finding in diverse conditions ranging from DGBI to GI motility, connective tissue and neurodegenerative disorders (1). A wide spectrum of signs and symptoms have been attributed to SIBO (1,2). Diagnosis is achieved either by direct culture of duodenal aspirate or indirectly, by demonstrating exhaled fermentation gases with ingested sugars, such as glucose or lactulose (3,4). In the breath tests used for carbohydrate intolerances, the symptoms provoked are at least as important for the diagnostic interpretation as the measured gas concentrations. However, the symptoms generated during SIBO breath tests are neither evaluated nor mentioned in most testing guidelines. SIBO exists in asymptomatic populations and the association with symptoms remains uncertain (1,2).

Aims & Methods

We examined the acute relationship between breath gases and the symptoms generated during glucose breath tests in DGBI. A standardised breath test with glucose (50g in 150ml water) was performed after a 24-hour low-FODMAP diet and >8-hour fast. Exhaled hydrogen and methane concentrations were measured and symptom assessments (composite symptom index score, SI used for intolerance breath tests)(5) were performed every 15 minutes for 2 hours in 790 male (30%) and female patients of average age 40.0 years referred to our gastroenterology practice with DGBI (Rome 4 criteria). Breath gas concentration thresholds of >20ppm and >10ppm above baseline were considered positive tests for hydrogen and methane, respectively.

Results

Overall, 59 (7.5%) and 111 (14.1%) DGBI patients were SIBO positive using the hydrogen and methane thresholds, respectively. The composite SI was positive in 208 (26.3%) of patients. The most common individual symptoms were fullness, nausea, tiredness, headache (each in >30% of patients), followed by bloating, flatulence, abdominal cramps or pain, GORD and problems concentrating (each in 20-30% of patients). A positive SI with a negative hydrogen test was seen in 151 (19.1%) of DGBI patients, in 108 (13.0%) with a negative methane test and in 55 (7.0%) with both negative hydrogen and methane tests. A negative SI occurred in 2.4% of patients if either of the gas tests was positive.

Conclusion

During the glucose SIBO breath test, positive gas results and evoked symptoms are closely associated. However, glucose frequently provokes symptoms in DGBI patients with negative hydrogen and/or methane breath test results. This may be due to a discrepancy between breath and intestinal gases, production of gases beyond hydrogen and methane, or the induction of symptoms by glucose or its metabolites via alternative mechanisms.

References

1. Quigley EMM, et al. Expert Review. Gastroenterology 2020;159:1526-1532.
2. Bushyhead D, et al. Gastroenterology 2022;163:593-607.
3. Losurdo G, et al. J Neurogastroenterol Motil 2020;26:16-28.
4. Tansel A, et al. Clin Transl Gastroenterol 2023;14:e00567.
5. Wilder-Smith CH, et al. Aliment Pharmacol Ther 2013;37:1074-83.