Reassessing Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome: A Comparative Study of Diagnostic...

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.

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.

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.

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.