Evaluation of small intestinal bacterial overgrowth

ABSTRACTIntroduction There has been phenomenal interest concerning gut microbiota dysbiosis including small intestinal bacterial overgrowth (SIBO). However, the diagnostic methods for SIBO are still unsatisfactory.Areas covered The current review covers the different invasive and noninvasive tests to diagnose SIBO, their methodology, interpretation, sensitivity, specificity, and limitations based on the selected articles from literature search using searchterms ‘small intestinal bacterial overgrowth’ AND ‘digestive diseases’ OR‘diagnosis’ OR ‘hydrogen breath test’ in PubMed in December 2022. The current review will cover some potential methods for diagnosis of SIBO that may be of clinical utility in the future.Expert opinion SIBO was conventionally defined as a total bacterial count >105 colony forming units (CFU) per mL on quantitative culture of upper gut aspirate. The threshold for the diagnosis of SIBO has been reduced to >103CFU per mL of aspirate recently. Considering the invasiveness of collecting upper gut aspirate, need for laboratory infrastructure and manpower to culture it, noninvasive hydrogen breath tests (HBT) became popular. However, due to the poor sensitivity and specificity of HBT to diagnose SIBO, their utility is being challenged. A new technology of measuring intra-luminal hydrogen gas has a potential to bring a paradigm shift in the diagnostic tests for SIBO.KEYWORDS: Gut microbiotarifaximinhydrogen breath testdisorders of gut-brain interactionFunctional Gastrointestinal disorders Article highlights Gut microbiota dysbiosis including small intestinal bacterial overgrowth (SIBO) is common in several digestive and extra-digestive disorders.Though quantitative upper gut aspirate culture using a double-lumen catheter to prevent oro-pharyngeal contamination is the current ‘gold standard’ for the diagnosis of SIBO, it has limitations such invasiveness, needs for high-level microbiology laboratory, cost and inability to culture 70% of gut microbes.Though hydrogen breath tests are quite popular to diagnose SIBO, these are neither sensitive nor specific limiting their clinical utility.Search for better tests for diagnosis of SIBO continues, some of which are elaborated in this review.Declaration of interestUCG holds the patent for double-lumen catheter assembly for upper gut aspirate culture, FODMAP fermentation chamber, and BreathCalc. GH report to be on the advisory boards of Australian Biotherapeutics, Glutagen, Bayer and received research support from Bayer, Abbott, Pfizer, Janssen, Takeda, Allergan. He serves on the Boards of the West Moreton Hospital and Health Service, Queensland, UQ Healthcare, Brisbane, and the Gastro-Liga, Germany. He has a patent for the Brisbane aseptic biopsy device and serves as Editor of the Gastro-Liga Newsletter. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.Reviewers disclosurePeer reviewers on this manuscript have no relevant financial relationships or otherwise to disclose.Additional informationFundingThis paper was not funded.