Breath tests in the diagnosis of small intestinal bacterial overgrowth in patients with irritable bowel syndrome in comparison with quantitative upper gut aspirate culture

Background Small intestinal bacterial overgrowth (SIBO) is reported in 4–78% patients with irritable bowel syndrome (IBS). This wide range of percentages might be because of the different techniques and criteria used to define the condition. We studied the utility of early (breath hydrogen increase 20 ppm above basal within 90 min) and double peaks on lactulose and glucose hydrogen breath tests (LHBT and GHBT, respectively) to diagnose SIBO (gold standard: upper gut aspirate culture). We also studied the clinical parameters that are associated with SIBO among them. Methods Overall, 80 patients with IBS (Rome 3) were evaluated for SIBO using aspirate culture, GHBT, and LHBT (with methane). Results A total of 15/80 (19%) patients had SIBO (≥105 CFU/ml) on culture compared with 0/10 historical controls; 4/15 (27%) with and none of 65 without SIBO had positive GHBT (sensitivity 27%, specificity 100%). None of 15 with and one of 65 without SIBO had double peaks on LHBT (sensitivity 0%, specificity 98%); 5/15 (33%) with and 23/65 (35%) without SIBO had an early peak on LHBT (sensitivity 33%, specificity 65%); and 2/15 (13.3%) with and 26/63 (41.3%) without SIBO had high methane on LHBT (sensitivity 13.3%, specificity 58.7%). Patients with SIBO on culture more often had diarrhea [6/15 (40%) vs. 8/65 (12.3%), P=0.011], higher weekly stool frequency [21 (3–28) vs. 14 (4–49), P=0.003], and looser forms [Bristol 5–6, 11/15 (73.3%) vs. 33/65 (50.8%), P=0.116]. Conclusion On the basis of culture, 19% patients with IBS had SIBO. The specificity of GHBT was 100%, but the sensitivity of this test and the diagnostic performances of LHBT and breath methane were all very poor. SIBO was more common in IBS patients with diarrhea than in patients with other bowel habits.