Reassessing Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome: A Comparative Study of Diagnostic Guidelines and Their Clinical Relevance

BACKGROUND/AIMS: Hydrogen breath testing is a widely used, noninvasive method for diagnosing small intestinal bacterial overgrowth. However, diagnostic cut-offs vary across international guidelines. This study evaluated the diagnostic performance of differing criteria. METHODS: We prospectively studied consecutive adults with irritable bowel syndrome who underwent glucose hydrogen breath testing. Small intestinal bacterial overgrowth was diagnosed using the Asia-Pacific consensus (rise in hydrogen ≥ 12 ppm from baseline) and the North American consensus (rise ≥ 20 ppm). Methane ≥ 10 ppm was considered methane-positive in both. RESULTS: Ninety subjects were included (median age 49 years; 53% female); 60% had diarrhea-predominant subtype. Small intestinal bacterial overgrowth was diagnosed in 44.4% using Asia-Pacific criteria and 37.8% using North American criteria. Hydrogen-positive cases were significantly associated with diarrhea-predominant subtype, while methane-positive cases correlated with constipation-predominant subtype. Severe irritable bowel syndrome symptoms (Symptom Severity Scale > 300) were more common in affected patients based on both Asia-Pacific (32.5% vs. 8.0%, p = 0.003) and North American (29.4% vs. 12.5%, p = 0.047) criteria. Only the Asia-Pacific criteria were significantly associated with higher symptom severity scores (median: 200 vs. 165, p = 0.009), whereas this was not significant with the North American criteria (median: 200 vs. 170, p = 0.087). Small intestinal bowel overgrowth was also linked to poorer quality of life and higher depression rates. CONCLUSION: The Asia-Pacific consensus diagnostic criteria improved detection and identified cases associated with more severe irritable bowel syndrome. These findings support using a lower hydrogen cut-off for breath testing, particularly in Asian populations.