Improving the serum D-xylose test for the identification of patients with small intestinal malabsorption

Background: D-Xylose absorption testing is a simple, low-cost method of scr eening for small intestinal malabsorption. The optimum method to measure D- xylose absorption (serum us. urine testing) is uncertain. Goals: We present a method of improving the accuracy of D-xylose testing. Study: Fifty-one c onsecutive patients (40 with chronic diarrhea and 5 asymptomatic patients w ith renal insufficiency) and 6 volunteers with normal renal function were r ecruited. All received D-xylose, 10 g intravenously and 25 mg orally,, on t wo separate occasions. Serum concentration was determined at baseline and a t frequent times thereafter. Area under the curve was calculated to infinit y, and D-xylose bioavailability (F) was calculated. A nonlinear model used to derive the relationship between S-hour D-xylose concentrations and F sho wed that a value of less than 22.5 mg/dL correlated with an F of less than 60% (malabsorption of D-xylose). A 1-hour D-xylose of less than 20 mg/dL wa s considered abnormal. Results: Using these indexes for normal 1- and 3-hou r D-xylose levels, 90% of patients with D-xylose malabsorption were identif ied (sensitivity, 90%; specificity, 95%), which represents a marked improve ment within the conventional 1-hour D-xylose of less than 20 mg/dL alone (s ensitivity, 71%; specificity, 100%). The model was applied prospectively to 15 additional patients with chronic diarrhea. Of these, 12 patients with a n F of less than 60% were identified, including 2 patients with normal 1-ho ur D-xylose levels. Conclusions: Thus, the addition of a 3-hour D-xylose se rum level of less than 22.5 mg/dL to conventional 1-hour D-xylose determina tion greatly improves the D-xylose test for malabsorption screening.