Background: Small intestinal bacterial overgrowth (SIBO) is defined as the presence of excessive and abnormal types of bacteria in the small intestine. SIBO has been linked to several gastrointestinal and extraintestinal diseases. While small bowel aspiration and culture is the accepted gold standard for diagnosis, glucose breath testing (GBT) is widely used in the routine clinical setting. We aimed to prospectively compare in the routine clinical setting results of the GBT with duodenal aspirate and culture for diagnosing SIBO.
Methods: We prospectively recruited patients between 2019-2023 with clinical suspicion of SIBO who underwent GBT as well as a gastroscopy and aspirate collected from the third part of the duodenum and cultured utilizing previously published methods (1). We used the threshold of >10^3 colony forming units (cfu)/ml of bacteria in aspirates obtained from the D3 for diagnosing SIBO. Similarly a positive GBT for SIBO was defined as rise over baseline >20 parts per million (ppm) for hyfrogen and/or rise over baseline by 10 ppm for methane. We calculated the sensitivity, specificity, positive and negative predictive value for the GBT against the duodenal aspirate and culture.
Results: The final dataset included 131 patients with suspected SIBO who underwent GBT and had duodenal aspirate collected. The cohort had an average age of 43.2 ±15.6 years, with 73% female. Based upon duodenal aspirates and culture, 51 (38.9%, 95% CI 30.5-47.8) patients were positive for SIBO, at a cut off threshold of ≥10³colony forming units of bacteria/ml (Table 1). In contrast based upon the GBT, 13/131 (9.9%, 95% CI 5.4-16.4) tested positive for SIBO. Compared with the reference standard of small bowel aspirate and culture, GBT had accuracy of 55.7% (sensitivity 5.9%, specificity 87.5%).
Conclusion: The results of this large prospective single centre study shows that GBT has poor sensitivity but good specificity when compared to duodenal aspirate and culture for diagnosing SIBO. However, there is lack of universal acceptance and validation of small bowel aspirate and culture as the gold standard for diagnosing SIBO. This highlights the urgent need to develop better validated diagnostic tests for SIBO in routine clinical settings.
References:
1. Shah A, Talley NJ, Koloski N, Macdonald GA, Kendall BJ, Shanahan ER, et al. Duodenal bacterial load as determined by quantitative polymerase chain reaction in asymptomatic controls, functional gastrointestinal disorders and inflammatory bowel disease. Alimentary pharmacology & therapeutics. 2020;52(1):155-67.

Teressa Hansen

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