What is the recommended workup and treatment for Small Intestine Bacterial Overgrowth (SIBO)?

SIBO Workup and Treatment

Diagnostic Approach

When SIBO is suspected, testing rather than empirical treatment should be used whenever possible to establish the diagnosis and support antibiotic stewardship, particularly in patients where multiple diagnoses may coexist. 1

First-Line Diagnostic Testing

• Combined hydrogen and methane breath testing is the recommended first-line non-invasive diagnostic method, as it is more accurate than hydrogen-only testing 1, 2, 3
• Glucose breath test (GBT) is more specific (83.2-92.3%) than lactulose breath test (LBT), though GBT has slightly lower sensitivity (54.5-71.4% vs 85.7%) 4, 5
• Use a glucose dose of 75g or lactulose dose of 10g for breath testing 1
• A delta H2 cut-off lower than >20 ppm shows better diagnostic performance (sensitivity 61.7%, specificity 86.0%) compared to the traditional >20 ppm cut-off 5

Gold Standard (When Breath Testing Inadequate)

• Jejunal aspirate with quantitative culture (≥10⁵ CFU/mL) remains the gold standard but is invasive and not routinely available 1, 6
• For qualitative assessment at endoscopy: flush 100 mL sterile saline into duodenum, wait a few seconds, then aspirate ≥10 mL into sterile trap; positive aspirates will grow colonic bacteria 1
• Common species include Bacteroides, Enterococcus, and Lactobacillus 1

Important Caveats

• Breath tests lack standardization and have poor sensitivity/specificity in many contexts 1
• False positives can occur with rapid small intestinal transit 2
• False negatives occur because most relevant bacteria cannot be cultured 1
• Lack of response to empirical antibiotics may indicate resistant organisms, absence of SIBO, or coexisting disorders 1, 2

Clinical Presentation

Look for these specific features:

• Bloating, abdominal distension, diarrhea, abdominal pain 2, 6
• Weight loss or malnutrition 1
• Nausea or vomiting 1

High-Risk Populations

• Post-Crohn's disease resection (30% prevalence) 1, 2
• Patients with blind loops, dysmotility, diverticulae, or strictures 1
• Loss of ileocecal valve 2
• Structural GI tract changes 2
• Proton-pump inhibitor or opioid use 7

Treatment Algorithm

First-Line Antibiotic Therapy

Rifaximin 550mg twice daily for 1-2 weeks is the most effective treatment with 60-80% efficacy in proven SIBO. 1, 2, 3

• Rifaximin is preferred as a non-absorbed antibiotic, reducing systemic resistance risk 1
• Alternative antibiotics with similar efficacy: doxycycline, ciprofloxacin, amoxicillin-clavulanic acid, or cefoxitin 1, 2
• Metronidazole is less effective and should be avoided 1, 2

Dietary Management (Adjunctive)

• Reduce fermentable carbohydrates (FODMAPs) for 2-4 weeks 2, 8
• Ensure adequate protein intake while reducing fat consumption to minimize steatorrhea 2, 8
• Consume complex carbohydrates and fiber to support gut motility 2, 8
• Plan 4-6 small meals daily rather than 3 large meals 2, 8
• Separate liquids from solids (avoid drinking 15 minutes before or 30 minutes after eating) 2, 8

Management of Recurrent SIBO

For patients with reversible causes (e.g., immunosuppression during chemotherapy), one antibiotic course usually suffices 1

For recurrent SIBO, consider:

• Rotating antibiotics with 1-2 week antibiotic-free periods 3
• Cyclical antibiotics 1
• Low-dose long-term antibiotics 1

Screening for Complications

Nutritional Deficiencies

• Screen for fat-soluble vitamins (A, D, E, K) deficiency due to bacterial deconjugation of bile salts 2, 8
• Check vitamin B12 and iron status 8
• Monitor for vitamin D deficiency in patients on bile acid sequestrants (occurs in 20%) 1

Coexisting Conditions

• Consider bile salt malabsorption if steatorrhea persists; treat with bile acid sequestrants (colestyramine, colesevelam) 1, 2, 8
• Evaluate for pancreatic exocrine insufficiency, which may coexist with SIBO 2
• If pancreatic enzyme replacement therapy is poorly tolerated, this often indicates underlying SIBO; once SIBO is eradicated, enzyme therapy is usually better tolerated 2

Critical Warning Sign

• If numbness or tingling in feet develops while on antibiotics, stop immediately and contact physician as this indicates peripheral neuropathy 8

Common Pitfalls

• Using antimotility agents when bowel dilation has occurred can worsen diarrhea by encouraging bacterial overgrowth 3
• Continuing probiotics during antimicrobial treatment may counteract therapeutic effects 3
• Falsely low fecal elastase may occur secondary to diarrhea when screening for pancreatic insufficiency 2
• Bile acid sequestrants can worsen vitamin deficiencies 8