Small intestinal bacterial overgrowth is the abnormal presence of excessive numbers of bacteria in the small intestine.

Small intestinal bacterial overgrowth is a condition in which the small bowel is colonized by excessive numbers of aerobic and anaerobic microbes that are normally found in the large intestine.

SIBO is characterized by a wide spectrum of clinical manifestations, ranging from unspecific, “functional” abdominal symptoms (e.g., bloating, abdominal discomfort, and flatulence) to less frequent severe generalized malabsorption and nutrient deficiency (diarrhea, anemia, deficiency of vitamins, and iron, steatorrhea, weight loss).

Interpretation of hydrogen breath test

• A H2 cut‐off ≥ 20 parts per million increase above baseline at a single time point during the test shall indicate maldigestion or malabsorption.

• Several factors affecting the intestinal microbiota, gut motility and the individual sensitivity may result in false positive and false negative results:

• False negative results for carbohydrate malabsorption by breath testing may occur in patients with low H2 excretion (H2 non‐excretion is reported in up to 10% of patients), in those with slow oro‐cecal transit time in whom carbohydrate fermentation commences after conclusion of the breath test and in patients with elevated baseline H2 concentration.

• False positive results for carbohydrate malabsorption by breath testing may occur in small intestinal bacterial overgrowth or in rapid oro‐cecal transit time.