Refined Lactulose Hydrogen Breath Test for Small Intestinal Bacterial Overgrowth Subgrouping Irritable Bowel Syndrome With Low and High Breath Hydrogen

<b>Background:</b> Small intestinal bacterial overgrowth (SIBO) is suggested in irritable bowel syndrome (IBS). Our primary aim was to define a discriminating threshold for a positive lactulose hydrogen breath test (LHBT) in SIBO. As a secondary aim, IBS was subdivided into SIBO and non-SIBO groups. <b>Methods:</b> LHBT performed in 206 subjects, 74 healthy subjects, 39 SIBO patients with intestinal lesions, 77 IBS patients, and 16 nonhydrogen producers. Using scintigraphy and LHBT, orocecal transit time was set to 80 min. Peak hydrogen levels were compared between the groups. Values are mean and 95% confidence interval. <b>Results:</b> Using an 80-min orocecal cutoff time, LHBT in healthy subjects had peak values of 8 (6-9) ppm and SIBO 38 (31-45) ppm (<i>p</i> < 0.0001). The diagnostic cutoff 20 ppm verified a sensitivity of 77% and specificity of 88% and positive and negative predictions of 77% and 88%. With the same cutoff for IBS, the mean peak value was 21 (16-26) ppm (<i>p</i> < 0.0001 vs. healthy) with a sensitivity of 39% and a specificity of 78% and positive and negative predictions of 77% and 84%. Separating IBS at 20 ppm, the low-hydrogen group had a peak value of 6 (5-7) ppm (ns vs. healthy), and the high-hydrogen group had a peak of 44 (38-49) ppm (<i>p</i> < 0.0001 vs. healthy). After antibiotics, IBS with low hydrogen remained unchanged, whereas those with high hydrogen were reduced to control (<i>p</i> < 0.01). <b>Conclusion:</b> With cutoff at 20 ppm, LHBT differentiates SIBO in patients with early high breath hydrogen peaks, subdividing IBS into non-SIBO and SIBO groups; the latter may benefit from antibiotic treatment.