Diagnostic Approach for Small Intestinal Bacterial Overgrowth (SIBO)

Primary Diagnostic Strategy

The American Gastroenterological Association recommends beginning with hydrogen and methane breath testing using glucose or lactulose as the first-line diagnostic approach, as this is non-invasive, cost-effective, and sufficiently accurate for clinical practice 1, 2
Combined hydrogen and methane breath testing is more effective at identifying both hydrogen-producing bacteria and methane-producing archaea than hydrogen alone 2

Patients with Crohn's disease, particularly those with stricturing or fistulizing phenotype, hypomotility, or loss of ileocecal valve, are at high risk for SIBO, with a prevalence of up to 30% 1
The European Society for Clinical Nutrition and Metabolism suggests that patients with severe chronic small intestinal dysmotility, gut stasis, or dilated bowel with reduced propulsion should be tested for SIBO 3
The American College of Gastroenterology recommends testing for SIBO in patients with symptoms such as abdominal pain, bloating, diarrhea, and flatulence 1

The British Society of Gastroenterology recommends identifying predisposing conditions such as gastric acid suppression, intestinal dysmotility, absent ileocecal valve, immunodeficiency, or reduced pancreatic/biliary secretions before performing diagnostic tests 3
The American Gastroenterological Association suggests performing combined hydrogen-methane breath testing with glucose substrate as the first choice, or lactulose if glucose is unavailable 1, 2

The European Society for Clinical Nutrition and Metabolism advises against relying on traditional culture threshold of >10⁵ CFU/mL as the sole diagnostic criterion; ≥10³ CFU/mL with colonic-type bacteria may indicate SIBO 1
The American College of Gastroenterology recommends avoiding lactulose breath testing in patients with rapid small bowel transit, as this affects test interpretation and may yield false positives 1

The American Gastroenterological Association notes that fat-soluble vitamin deficiencies, particularly vitamins A and E, may be indicative of SIBO due to bacterial deconjugation of bile salts 3
The British Society of Gastroenterology suggests that vitamin B12 malabsorption may be a sign of SIBO 3
The European Society for Clinical Nutrition and Metabolism recommends testing for high anion gap acidosis from D-lactic acid production, which may be indicative of SIBO 3, 4