title: The lactulose breath hydrogen test and small intestinal bacterial overgrowth.
abstract: OBJECTIVE
  To i) document the sensitivity and specificity of a combined scintigraphic/lactulose breath hydrogen test for small intestinal bacterial overgrowth and ii) investigate the validity of currently accepted definitions of an abnormal lactulose breath hydrogen test based on "double peaks" in breath hydrogen concentrations.
  
  
  METHODS
  Twenty-eight subjects were investigated with culture of proximal small intestinal aspirate and a 10-g lactulose breath hydrogen test combined with scintigraphy. Gastroduodenal pH, the presence or absence of gastric bacterial overgrowth, and the in vitro capability of overgrowth flora to ferment lactulose were determined.
  
  
  RESULTS
  Sensitivity (16.7%) and specificity (70.0%) of the lactulose breath hydrogen test alone for small intestinal bacterial overgrowth were poor. Combination with scintigraphy resulted in 100% specificity, because double peaks in serial breath hydrogen concentrations may occur as a result of lactulose fermentation by cecal bacteria. Sensitivity increased to 38.9% with scintigraphy, because a single rise in breath hydrogen concentrations, commencing before the test meal reaches the cecum, may occur in this disorder. Sensitivity remained suboptimal irrespective of the definition of small intestinal bacterial overgrowth used, the nature of the overgrowth flora, favorable luminal pH, the presence of concurrent gastric bacterial overgrowth, or the in vitro ability of the overgrowth flora to ferment lactulose.
  
  
  CONCLUSIONS
  Definitions of an abnormal lactulose breath hydrogen test based on the occurrence of double peaks in breath hydrogen concentrations are inappropriate. Not even the addition of scintigraphy renders this test a clinically useful alternative to culture of aspirate for diagnosing small intestinal bacterial overgrowth.
authors.affiliation: Department of Gastroenterology, Prince of Wales Hospital, Sydney, Australia.
authors.forename: S M
authors.initials: SM
authors.lastname: Riordan
authors.forename: C J
authors.initials: CJ
authors.lastname: McIver
authors.forename: B M
authors.initials: BM
authors.lastname: Walker
authors.forename: V M
authors.initials: VM
authors.lastname: Duncombe
authors.forename: T D
authors.initials: TD
authors.lastname: Bolin
authors.forename: M C
authors.initials: MC
authors.lastname: Thomas
mesh_terms: D001424:Bacterial Infections / Q000175:diagnosis* / Q000000981:diagnostic imaging; D001944:Breath Tests; D005285:Fermentation; D006801:Humans; D006859:Hydrogen / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000382:microbiology*; D007792:Lactulose / Q000378:metabolism; D008875:Middle Aged; D011877:Radionuclide Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013270:Stomach / Q000382:microbiology
chemical_list: D007792:Lactulose; D006859:Hydrogen