title: Breath testing to evaluate lactose intolerance in irritable bowel syndrome correlates with lactulose testing and may not reflect true lactose malabsorption.
abstract: OBJECTIVE
  An increased prevalence of lactose intolerance is seen in irritable bowel syndrome (IBS). Recently, we demonstrated a high prevalence of abnormal lactulose breath test results in IBS suggesting bacterial overgrowth. Because symptoms of lactose intolerance result from bacterial fermentation, the purpose of this study was to determine whether an abnormal lactose breath test is reflective of malabsorption or early presentation to bacteria.
  
  
  METHODS
  Subjects with diarrhea-predominant IBS were enrolled. On day 1, subjects underwent a lactulose breath test after an overnight fast. Within 1 wk, subjects returned after fasting for a lactose breath test with simultaneous blood glucose measurements every 15 min to complete a lactose tolerance test (LTT). Symptoms were evaluated 3 h after lactose administration.
  
  
  RESULTS
  Twenty subjects completed the study. One subject inadvertently received dextrose through the intravenous and was excluded. Of the remaining 19 subjects, three (16%) had an abnormal LTT suggesting malabsorption. In all, 10 subjects (53%) had an abnormal lactose breath test, 14 (74%) had an abnormal lactulose breath test, and 11 (58%) had symptoms after lactose administration. The agreement with symptoms was moderate (kappa = 0.47) and fair (kappa = 0.24) when compared to the lactose breath test and LTT, respectively. There was a fair correlation between lactose breath test and LTT (kappa = 0.29). However, lactose breath test hydrogen levels >166 ppm were universally predictive of abnormal LTT. Finally, a significant correlation was seen between the hydrogen production on lactose and lactulose breath test (r = 0.56, p = 0.01).
  
  
  CONCLUSIONS
  Lactose breath testing in IBS subjects does not seem to reflect malabsorption; it may be an indicator of abnormal lactulose breath test, suggesting bacterial overgrowth.
authors.affiliation: GI Motility Program, Department of Medicine, CSMC Burns and Allen Research Institute, Cedars-Sinai Medical Center, 8635 W. 3rd Street, Suite 770, Los Angeles, CA 90048, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Pimentel
authors.forename: Yuthana
authors.initials: Y
authors.lastname: Kong
authors.forename: Sandy
authors.initials: S
authors.lastname: Park
mesh_terms: D000328:Adult; D001944:Breath Tests; D003951:Diagnostic Errors; D005260:Female; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000150:complications*; D007787:Lactose Intolerance / Q000150:complications* / Q000175:diagnosis*; D007792:Lactulose / Q000032:analysis; D016014:Linear Models; D008297:Male; D011237:Predictive Value of Tests
chemical_list: D007792:Lactulose