Small-bowel aspiration during upper esophagogastroduodenoscopy: Rao technique

Understanding Our Tests: Hydrogen-Methane Breath Testing to Diagnose Small Intestinal Bacterial Overgrowth

There is increasing appreciation that small intestinal bacterial overgrowth (SIBO) drives many common gastrointestinal symptoms, including diarrhea, bloating, and abdominal pain. Breath testing via measurement of exhaled hydrogen and methane gases following ingestion of a readily metabolized carbohydrate has become an important noninvasive testing paradigm to help diagnose SIBO. However, because of a number of physiological and technical considerations, how and when to use breath testing in the diagnosis of SIBO remains a nuanced clinical decision. This narrative review provides a comprehensive overview of breath testing paradigms including the indications for testing, how to administer the test, and how patient factors influence breath testing results. We also explore the performance characteristics of breath testing (sensitivity, specificity, positive and negative predictive values, likelihood ratios, and diagnostic odds ratio). Additionally, we describe complementary and alternative tests for diagnosing SIBO. We discuss applications of breath testing for research. Current estimates of SIBO prevalence among commonly encountered high-risk populations are reviewed to provide pretest probability estimates under a variety of clinical situations. Finally, we discuss how to integrate breath test performance characteristics into clinical care decisions using clinical predictors and the Fagan nomogram.

Small Intestinal Bacterial Overgrowth-Pathophysiology and Its Implications for Definition and Management

The concept of small intestinal bacterial overgrowth (SIBO) arose in the context of maldigestion and malabsorption among patients with obvious risk factors that permitted the small bowel to be colonized by potentially injurious colonic microbiota. Such colonization resulted in clinical signs, symptoms, and laboratory abnormalities that were explicable within a coherent pathophysiological framework. Coincident with advances in medical science, diagnostic testing evolved from small bowel culture to breath tests and on to next-generation, culture-independent microbial analytics. The advent and ready availability of breath tests generated a dramatic expansion in both the rate of diagnosis of SIBO and the range of associated gastrointestinal and nongastrointestinal clinical scenarios. However, issues with the specificity of these same breath tests have clouded their interpretation and aroused some skepticism regarding the role of SIBO in this expanded clinical repertoire. Furthermore, the pathophysiological plausibility that underpins SIBO as a cause of maldigestion/malabsorption is lacking in regard to its purported role in irritable bowel syndrome, for example. One hopes that the application of an ever-expanding armamentarium of modern molecular microbiology to the human small intestinal microbiome in both health and disease will ultimately resolve this impasse and provide an objective basis for the diagnosis of SIBO.

Bacterial overgrowth and lactose intolerance: how to best assess

PURPOSE OF REVIEW

To provide an up-to-date review on the clinical assessment of two important gastrointestinal problems with overlapping symptomatology but diverse cause and testing methods. Small intestinal bacterial overgrowth (SIBO) is characterized by the presence of excess bacteria in the small intestine associated with bloating, distention, gas, and diarrhea. Lactose intolerance is caused by lactase enzyme deficiency in the small bowel mucosa leading to lactose malabsorption and symptoms of bloating, gas, and diarrhea.

RECENT FINDINGS

SIBO is assessed by hydrogen/methane breath test using glucose as a substrate and/or small bowel aspirate and culture but these tests have shortcomings. Consequently, several new diagnostic techniques, including novel capsule technologies and other approaches are being evaluated. Lactose intolerance can be assessed by hydrogen/methane breath test using lactose as a substrate, or small bowel mucosal lactase assay, genetic testing and lactose tolerance test, although the efficacy and practicality of these diagnostic modalities are not equal.

SUMMARY

In clinical practice, gas, bloating, distention, pain, and diarrhea are common gastrointestinal symptoms that often remain unexplained when routine gastrointestinal endoscopy, imaging, and stool tests are negative. These patients should be evaluated for SIBO and/or food intolerances including lactose intolerance.