GI Endoscopy · 1 min read
Hydrogen Breath Testing for SIBO and Carbohydrate Malabsorption
A gastroenterologist can test for food intolerance through various methods, including elimination diets, hydrogen breath tests, and food allergy testing.
Clinical Bottom Line
| Substrate Specificity | Clinical Indication | Diagnostic Threshold |
|---|---|---|
| Lactulose | Small Intestinal Bacterial Overgrowth (SIBO). | Rise in Hydrogen ≥ 20 ppm over baseline within 90 mins. |
| Lactose | Lactase deficiency (Lactose Intolerance). | Similar rise in Hydrogen correlating directly with clinical symptoms (gas/bloating). |
| Fructose | Dietary Fructose Intolerance. | Confirmation dictates highly restrictive FODMAP dietary modification. |
Moving Beyond Symptom Diaries
Endoscopy provides brilliant structural evaluation but is entirely inert regarding metabolic or physiological intolerances. Bloating, massive gas production, and osmotic diarrhea often stalk patients suffering from carbohydrate malabsorption or Small Intestinal Bacterial Overgrowth (SIBO). Accurate diagnosis historically relied on unreliable symptom exclusion diets; 2026 standards mandate precise, non-invasive breath testing.
The Microbiology of Breath
Mammalian cells do not produce hydrogen or methane gas. When a patient ingest a concentrated substrate (e.g., lactulose), their small bowel should rapidly absorb it (or it shouldn't ferment if it sits). If a massive bacterial colony pathologically resides in the jejunum (SIBO), the bacteria immediately ferment the sugar, producing heavy hydrogen gas. This gas rapidly diffuses into the splanchnic circulatory system, travels to the lungs, and is exhaled. Spikes in exhaled hydrogen parts-per-million (ppm) objectively map the location and severity of the bacterial overload, driving the decision to administer non-absorbable antibiotics like Rifaximin.
Clinical guidelines summarized by the Gastroscholar Research Team. Last updated: 2026. This article is intended for physicians.
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