SIBO Testing Guide: Breath Tests Lab Tests and How to Get Diagnosed
SIBO Testing Guide: Breath Tests, Lab Tests, and How to Get Diagnosed
By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante
Key Takeaways
- The lactulose or glucose breath test is the primary non-invasive diagnostic tool for SIBO
- Breath tests measure hydrogen and methane gas produced by bacteria — elevated levels indicate bacterial overgrowth
- Hydrogen-dominant SIBO typically causes diarrhea; methane-dominant SIBO (now called IMO) causes constipation
- Proper test preparation (24-hour diet restriction + 12-hour fast) is CRITICAL for accurate results
- False negatives are common — a negative breath test does not definitively rule out SIBO
Types of SIBO Tests
1. Lactulose Breath Test (Most Common)
How it works: You drink a lactulose solution (a non-absorbable sugar). As it passes through the small intestine, bacteria ferment it and produce hydrogen and/or methane gas. You breathe into collection tubes every 15-20 minutes for 3 hours. The gas levels are measured.
Positive result (North American Consensus):
- Hydrogen rise ≥20 ppm above baseline within 90 minutes
- Methane ≥10 ppm at any point during the test
- Combined hydrogen + methane ≥15 ppm within 90 minutes (newer criteria)
Advantages: Tests the entire small intestine (lactulose reaches the distal ileum before entering the colon). Can detect both hydrogen and methane SIBO. Available at home (mail-order kits) and in-office.
Limitations: Lactulose itself can cause symptoms (bloating, gas) during the test. The transit time varies between individuals, making it hard to distinguish small intestinal fermentation from early colonic fermentation.
2. Glucose Breath Test
How it works: Same principle, but uses glucose instead of lactulose. Glucose is absorbed in the upper small intestine, so it only tests the proximal (upper) small intestine.
Advantages: Higher specificity than lactulose — if positive, it is very likely SIBO. Fewer false positives.
Limitations: Only tests the upper small intestine. Misses distal SIBO (overgrowth in the lower small intestine), which may account for 30-40% of SIBO cases. Higher false negative rate.
3. Jejunal Aspirate Culture (Gold Standard — Rarely Used)
How it works: An endoscope is passed into the jejunum (middle small intestine) and fluid is aspirated and cultured for bacteria. A bacterial count >10^5 CFU/mL is diagnostic.
Advantages: Direct measurement. Gold standard. Can identify specific bacterial species.
Limitations: Invasive (requires endoscopy). Expensive. Only samples one location. The aspirate can be contaminated by oral bacteria during the procedure. Rarely performed outside research settings.
Test Preparation (Critical for Accuracy)
24 Hours Before the Test
Follow a restricted diet:
- Eat only: White rice, plain chicken or fish, eggs, clear broth, water
- Avoid: All high-fiber foods, beans, legumes, dairy, fruit, vegetables, bread, pasta, alcohol, sugar
- Purpose: Starves bacteria of fermentable substrates so baseline gas is low
12 Hours Before the Test
- Begin fasting (water only)
- No smoking (alters breath gas readings)
- No vigorous exercise (affects CO2 levels)
During the Test
- Sit quietly — no exercise, sleeping, or lying down
- No eating, drinking (other than the test solution), or brushing teeth
- Collect breath samples at the designated intervals (every 15-20 minutes)
Interpreting Results
Hydrogen-Dominant SIBO
High hydrogen levels indicate fermentation by hydrogen-producing bacteria (primarily E. coli, Klebsiella, Streptococcus). Associated with IBS-D (diarrhea-predominant) symptoms: loose stools, urgency, cramping, bloating.
Methane-Dominant (IMO — Intestinal Methanogen Overgrowth)
High methane levels indicate archaea (primarily Methanobrevibacter smithii) that convert hydrogen to methane. Methane slows gut transit. Associated with IBS-C (constipation-predominant) symptoms: constipation, straining, hard stools, bloating.
Hydrogen Sulfide SIBO
A newer category. Standard breath tests do not measure hydrogen sulfide. A "flat line" test (very low hydrogen AND methane despite symptoms) may indicate hydrogen sulfide SIBO. The Trio-Smart breath test measures all three gases.
What to Do After a Positive Test
- Treatment: Rifaximin (hydrogen SIBO), rifaximin + neomycin or metronidazole (methane/IMO), or herbal antimicrobials
- During treatment: Low FODMAP diet + digestive enzyme support
- After treatment: Prokinetic support for the migrating motor complex (MMC) to prevent relapse. Casa de Sante Regularity Companion supports MMC function.
- Microbiome restoration: Casa de Sante FODMAP Enzymes + Probiotics for post-treatment microbiome rebalancing
- Retest: 2-4 weeks after completing treatment to confirm clearance
🛒 SIBO Management Support
- Digestive Enzymes — During and after treatment
- Regularity Companion — MMC/prokinetic support to prevent SIBO relapse
- FODMAP Enzymes + Probiotics — Post-treatment microbiome restoration
Frequently Asked Questions
Can I take a SIBO breath test at home?
Yes. Multiple companies offer at-home breath test kits (Trio-Smart, Aerodiagnostics, Commonwealth Diagnostics). You collect breath samples at home following the preparation protocol and mail them to a lab. Results are typically available within 1-2 weeks. Insurance may or may not cover the test.
How accurate are SIBO breath tests?
Sensitivity: 50-70% (meaning 30-50% of SIBO cases may be missed). Specificity: 70-85% (meaning 15-30% of positive results may be false positives). Breath tests are imperfect, but they are the best non-invasive option available. Clinical correlation (symptoms + test results) is essential.
Medical Disclaimer: This article is for educational purposes only. SIBO diagnosis and treatment should be supervised by a gastroenterologist or functional medicine practitioner. Do not self-treat SIBO based on test results alone. Dr. Adegbola is the founder of Casa de Sante.
