D-XYLOSE HYDROGEN BREATH TESTS COMPARED TO ABSORPTION KINETICS IN HUMAN PATIENTS WITH AND WITHOUT MALABSORPTION

The D-xylose breath H-2 test may be useful in characterizing intestinal absorptive function, Our aim was to determine whether breath H-2 following D-xylose administration reflects the extent to which the D-xylose is absorbed by comparing it to a kinetic model of D-xylose absorption. Twenty-five subjects were studied. They ingested 15 g D-xylose on the first day and 25 g D-xylose on the third day, On the second day they received 10 g intravenous D-xylose along with 15 g oral lactulose. Multiple serum and urine samples were obtained for D-xylose content to calculate its rate constants and extent of absorption by multicompartmental analysis, Breath H-2 determinations were obtained every 15 min for 3 hr following the 15 g D-xylose and lactulose ingestion, Peak breath H-2 concentration correlated with extent of absorption (r = -0.787, P < 0.001), K-0, the rate constant for nonabsorptive loss (r = 0.744, P < 0.001), and 5-hr urine content (r = -0.705, P < 0.001). Area under the breath H-2 curve also correlated with these parameters: extent of absorption (r = -0.770, P < 0.001), K-0 (r = 0.662, P < 0.001), 5-hr urine content (r = -0.629, P < 0.012). Peak D-xylose breath H-2 to peak lactulose breath H-2 showed no correlation with extent of absorption. The extent of absorption was higher with the 15-g dose than the 25-g dose in all patients tested (P < 0.01), This was the result of decreased nonabsorptive loss (lower K-0), as the rate constant for absorption, K-a, was not statistically different (P > 0.05). Peak D-xylose breath H-2 can be used as an inverse estimate of D-xylose absorption, Lactulose breath H-2 cannot be used as a standard for comparison for D-xylose, The three compartment kinetic model for D-xylose absorption with passive absorption of this carbohydrate is supported by similar rate constants for absorption for the two D-xylose doses used. D-Xylose at 15 g may be a more appropriate dose than 25 g for H-2 breath testing as it does not lead to increased nonabsorptive losses.