Detection of bacterial overgrowth in IBS using the lactulose H2 breath test: comparison with 14C-D-xylose and healthy controls

Am J Gastroenterol. 2005 Jul;100(7):1566-70. doi: 10.1111/j.1572-0241.2005.40795.x.


OBJECTIVES Recent reports suggest bacterial overgrowth is commonly associated with irritable bowel syndrome (IBS) when diagnosed using the lactulose hydrogen breath test (LHBT). We employed this test to examine whether similar findings exist in a geographically distinct population of Rome II positive IBS patients and compared it to the 14C-D-xylose breath test, a test with acknowledged greater specificity for bacterial overgrowth.

Methods: In the first series, Rome II IBS patients underwent a 10 g lactulose breath test and a standardized 1 g 14C-D-xylose breath test and answered IBS symptom questionnaires. A positive test required an elevated breath hydrogen concentration within 90 min, two distinct peaks, and an increase >20 ppm. In a second series, control patients lacking gastrointestinal symptoms underwent a lactulose breath test. A positive test required an elevation of breath hydrogen >20 ppm within 90 or 180 min. These criteria were also applied to lactulose breath tests from IBS cases in series one.

Results: The IBS patients were predominantly female (64%) and most reported severe symptoms (80%). The majority had diarrhea predominant symptoms (63%) and only 3% were constipation predominant. In the first series, only 10% of patients had a positive lactulose breath test and 13% had a positive 14C-D-xylose test. In the second series, the number of abnormal LHBTs was much higher but no differences were found between IBS patients and controls.

Conclusion: The lactulose breath test did not reliably detect a common association between bacterial overgrowth and IBS in our patient population.

Publication types

  • Comparative Study
  • Evaluation Study

MeSH terms

  • Adult
  • Bacteria / growth & development*
  • Breath Tests / methods*
  • Carbon Radioisotopes
  • Case-Control Studies
  • Female
  • Humans
  • Hydrogen / analysis*
  • Irritable Bowel Syndrome / microbiology*
  • Lactulose*
  • Male
  • Middle Aged
  • Xylose*


  • Carbon Radioisotopes
  • Lactulose
  • Hydrogen
  • Xylose