Intraluminal Small-Intestinal Utilization of d-Xylose by Bacteria: A limitation of the d-xylose absorption test

Abstract

Poor correlation between tests of fat absorption and the d-xylose test was noted in patients with variants of the blind loop syndrome. In such patients manifesting inordinately low d-xylose urinary excretion, coliform bacteria were recovered from the upper small intestine which on in vitro incubation manifested the ability to utilize d-xylose for their own metabolism. Perfusion of the duodenum and about 1 foot of jejunum with 25 g of d-xylose was performed in 3 volunteers and in 1 suitably selected patient before and after the eradication of heavy coliform growth. Phenol red was used as a nonabsorbable marker during the perfusion studies. The results of the perfusion tests and the clinical correlations indicate that multigram quantities of xylose may disappear from the lumen of the small intestine in patients with excessive coliform growth, presumably because bacteria metabolize xylose as substrate for their own metabolism. In such patients urinary xylose measurements may lead to erroneously low estimates of xylose absorption.