Detection of Small Intestine Bacterial Overgrowth by Means of a 14C-D-Xylose Breath Test

Abstract

Breath excretion of 14CO2 after oral administration of '4C-xylose has been determined in patients with untreated small intestine bacterial overgrowth, normal control subjects, patients with malabsorption not due to overgrowth, and overgrowth patients after antibiotic therapy. Excessive catabolism of 25 g 14Cxylose to 14CO2 was noted in untreated overgrowth patients as contrasted to the other groups. However, an element of nonspecific colon bacterial catabolism of substrate was noted in both patients and controls, leading to an inadequate level of sensitivity and specificity. Reduction of the total dose of xylose to 1 g, with increased concentration of radioactive xylose in the small intestine and less osmotic-related passage of substrate to the colon, has led to improved sensitivity and specificity. The modified test allowed detection of all overgrowth patients by breath analysis at 30 and/or 60 min (except the few with markedly delayed gastric emptying). 99mTc Intestinal scans, performed simultaneously with 1 g xylose breath tests in some overgrowth patients, demonstrated the potential for elevated breath 14CO2 excretion to be due solely to catabolism of xylose by small intestinal bacteria. Both the simply determined breath 14CO2 concentration and the actually measured 14CO2 output were found to be comparable in detecting bacterial overgrowth. The one gram 14Cxylose breath test, employing determination of breath 14CO2 concentration at 30 and 60 min, allows practical, sensitive, and relatively specific screening for the presence of small intestine bacterial overgrowth.