Factors influencing the 1-g 14C-D-xylose breath test for bacterial overgrowth

To document the sensitivity of the 1-g 14C-D-xylose breath test for bacterial overgrowth and to investigate luminal and nonluminal factors that may influence breath 14CO2 levels and impact on the clinical utility of this test.

Thirty-five adult subjects were investigated for bacterial overgrowth by culture of gastric and small intestinal aspirates and by a 1-g 14C-D-xylose breath test. Body weight, gastroduodenal pH and the in vitro capability of overgrowth flora to ferment D-xylose were assessed. Serial breath 14CO2 levels were also recorded before and after the resolution of malabsorption in a subject with celiac disease to determine the importance of postabsorptive metabolism of this substrate.

Gastric and small intestinal bacterial overgrowth were present in 19/35 (54.3%) and 21/35 (60.0%) subjects, respectively. The positivity rate of culture of aspirate exceeded that of the 1-g 14C-D-xylose breath test. Endogenous CO2 production independently influenced breath 14CO2 levels. After excluding this influence, sensitivity of the 1-g 14C-D-xylose breath test for gastric bacterial overgrowth or small intestinal bacterial overgrowth was poor, even when overgrowth with specific "marker organisms" was considered. Poor sensitivity could not be explained by unfavorable luminal pH. Overgrowth flora were proven capable of in vitro D-xylose fermentation in 81.8% of subjects. Systemic and/or colonic metabolism of 1-g 14C-D-xylose appear to be important factors influencing results of the 1-g 14C-D-xylose breath test, especially in partial gastrectomy subjects.

The 1-g 14C-D-xylose breath test is not a suitable alternative to culture of aspirate for the investigation of subjects for bacterial overgrowth.