S3095 Subtypes of Intestinal Overgrowth in Clinical Practice: A Single Center Study

Introduction: Intestinal overgrowth is identified through the lactulose breath test (LBT) and presents with nonspecific symptoms such as bloating, changes in bowel habits, or abdominal discomfort. Intestinal overgrowth can be categorized into Hydrogen-dominant (H2-dominant), Methane-dominant (CH4-dominant), and Hydrogen-Methane-Dominant (H2-CH4-dominant). Limited data exists comparing the clinical profiles of these subtypes. This study aims to evaluate the prevalence of different overgrowth subtypes and assess whether presenting symptoms can be used to predict them. Methods: We conducted a retrospective study of 213 patients who had positive LBT results at a single academic outpatient gastroenterology clinic between December 2024 and May 2025. These tests were interpreted according to the 2017 North American Consensus. Data collected included demographics, presenting symptoms (bloating, diarrhea, constipation, nausea, and abdominal pain), comorbidities, and breath test results. Logistic regression was used to calculate odds ratios for symptom-based prediction of intestinal overgrowth subtype. Results: Of 213 patients, 187 (87.8.%) tested positive for intestinal overgrowth. CH4-dominant was the most common subtype (144/213, 67.6%), followed by H2-CH4-dominant (43/213, 20.2%). No patients had isolated H2-dominant intestinal overgrowth. The cohort was predominantly female (67.2%) and White (69%). Irritable bowel syndrome (IBS) was the most common comorbidity, seen in 69% of positive cases. Logistic regression revealed that none of the 5 symptoms were statistically significant predictors of overgrowth subtype (all P > .05). The strongest predictor was abdominal pain, with 33% lower odds in H2-CH4-dominant patients compared to CH4-dominant, though it was not significant (P = 0.268). Conclusion: Symptom profiles did not significantly distinguish between CH4-dominant and H2-CH4-dominant overgrowth, underscoring the importance of objective data when making a diagnosis and treating intestinal overgrowth. Notably, CH4-dominant overgrowth was highly prevalent, while H2-dominant cases were absent. Further analysis, such as geographic distribution or microbiome composition, may be beneficial in understanding the variation in prevalence of different subtypes. While the prevalence of intestinal overgrowth in the general population remains unknown, this data indicates that a substantial proportion of patients with IBS may have concurrent intestinal overgrowth and could benefit from testing.