D-xylose kinetics and hydrogen breath tests in functionally anephric patients using the 15-gram dose

Malabsorptive evaluation in renal failure is difficult because most absorptive testing requires urinary collections. Kinetic analysis of d-xylose absorption and d-xylose breath testing were performed in an effort to establish an effective absorption test in functionally anephric patients. We studied 13 fasting renal failure patients with no diarrhea or symptoms suggesting malabsorption on two separate nondialysis days after they received 15 g oral d-xylose on day 1 and 10 g IV on day 2. Serum collections were used to calculate the kinetic rate constants and extent of d-xylose absorption. After the oral d-xylose, end expiratory breaths were collected every 15 minutes for 3 hours and were analyzed for H2 with gas chromatography. Five subjects also allowed upper endoscopy and duodenal biopsy. The mean absorption rate constant (Ka) and bioavailability (F) were similar to published values for normal subjects using the 15-g dose (0.936 min(-1); range, 0.227-1.96; and 74%, range 46-99, respectively). Of the patients, 12 had normal 1-hour serum d-xylose concentrations (>20 mg/dL). There was no clear inverse correlation between the rate constant for absorption or bioavailability and peak breath hydrogen or the area under the curve for breath H2 versus time. Using 15 g oral d-xylose, mean bioavailability and absorption rate constants are normal in functionally anephric patients with no clinical evidence of malabsorption. Three patients had elevated breath peak H2 concentrations, but there was no clear inverse correlation between bioavailability and the breath H2 values. A 1-hour serum dxylose concentration >20 mg/dL may be considered normal in this patient group, similar to patients with normal renal function.