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 screening for small intestinal malabsorption. The optimum method to measure D-xylose absorption (serum vs. urine testing) is uncertain.


OBJECTIVE
We present a method of improving the accuracy of D-xylose testing.


METHODS
Fifty-one consecutive patients (40 with chronic diarrhea and 5 asymptomatic patients with renal insufficiency) and 6 volunteers with normal renal function were recruited. All received D-xylose, 10 g intravenously and 25 mg orally, on two separate occasions. Serum concentration was determined at baseline and at frequent times thereafter. Area under the curve was calculated to infinity, and D-xylose bioavailability (F) was calculated. A nonlinear model used to derive the relationship between 3-hour D-xylose concentrations and F showed 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 was considered abnormal.


RESULTS
Using these indexes for normal 1-and 3-hour D-xylose levels, 90% of patients with D-xylose malabsorption were identified (sensitivity, 90%; specificity, 95%), which represents a marked improvement within the conventional 1-hour D-xylose of less than 20 mg/dL alone (sensitivity, 71%; specificity, 100%). The model was applied prospectively to 15 additional patients with chronic diarrhea. Of these, 12 patients with an F of less than 60% were identified, including 2 patients with normal 1-hour D-xylose levels.


CONCLUSIONS
Thus, the addition of a 3-hour D-xylose serum level of less than 22.5 mg/dL to conventional 1-hour D-xylose determination greatly improves the D-xylose test for malabsorption screening.
Ehrenpreis
E D
ED
Division of Gastroenterology, Department of Medicine, University of Chicago Hospitals, 5841 South Maryland Avenue, Chicago, IL 60637, U.S.A.
Salvino
M
M
Craig
R M
RM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001682:Biological Availability; D002908:Chronic Disease; D003967:Diarrhea / Q000209:etiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D007421:Intestine, Small / Q000503:physiopathology; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000503:physiopathology; D007677:Kidney Function Tests; D008286:Malabsorption Syndromes / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008657:Metabolic Clearance Rate / Q000502:physiology; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012016:Reference Values; D014994:Xylose / Q000493:pharmacokinetics
D014994:Xylose