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Clinical manifestations and diagnosis of small intestinal bacterial overgrowth

Mark Pimentel, MD, FRCP(C)
Section Editor
J Thomas Lamont, MD
Deputy Editor
Shilpa Grover, MD, MPH, AGAF


Small intestinal bacterial overgrowth (SIBO) is a condition in which non-native bacteria and/or native bacteria are present in increased numbers resulting in excessive fermentation, inflammation, or malabsorption. It typically occurs in association with anatomical abnormalities, motility disorders, or multifactorial causes (eg, liver cirrhosis, chronic pancreatitis) (table 1).

The clinical manifestations and diagnosis of SIBO will be reviewed here. The etiology, pathogenesis, and treatment of SIBO are discussed in detail, separately. (See "Small intestinal bacterial overgrowth: Etiology and pathogenesis" and "Treatment of small intestinal bacterial overgrowth".)


The majority of patients with small intestinal bacterial overgrowth (SIBO) present with nonspecific symptoms of bloating, flatulence, or abdominal discomfort, or they may be asymptomatic. Many patients diagnosed with severe SIBO have diarrhea. Although classic SIBO descriptions include steatorrhea with greasy or bulky stools, this is uncommon and occurs principally if the SIBO is caused by altered anatomy such as blind loop syndrome [1]. Rarely, patients have weight loss due to severe diarrhea, malabsorption, or poor oral intake. Although diarrhea is a common symptom in children, they may present with chronic abdominal pain alone [2,3]. Children may also have evidence of malnutrition and may fail to gain weight. Patients with hypoalbuminemia due to malabsorption may have peripheral edema on physical examination.

Rarely, patients with SIBO may also present with symptoms and signs secondary to vitamin deficiencies. It is important to assess for these in subjects with severely altered anatomy causing SIBO, severe immunodeficiencies, or tropical sprue. These include:

Patients with vitamin A deficiency have xerophthalmia and night blindness, xerosis of the conjunctiva manifested as Bitot's spots, and follicular hyperkeratosis. (See "Overview of vitamin A", section on 'Clinical manifestations'.)


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Literature review current through: May 2017. | This topic last updated: Jan 25, 2016.
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