A Clinical Evaluation of the D-Xylose Tolerance Test

Abstract

The pentose sugar, d-xylose, appears to be a satisfactory test substance for the indirect measurement of intestinal absorption of carbohydrate. Considerable experience with the d-xylose tolerance test in malabsorption syndrome has accumulated in the literature. The xylose test response was studied in normal subjects at various ages and during steroid therapy; in simple diarrhea; in idio-pathic steatorrhea and in secondary steatorrhea. In addition, they have studied the test in illnesses associated with defects in metabolism and excretion but without defects in intestinal absorption. Technically, the test is simple to perform and is a valid and reproducible measure of carbohydrate absorption. In normal subjects, it is influenced by age and reflects the physiological depression of renal function. In active, untreated, adult idiopathic sprue, and in secondary steatorrhea due to extensive disease, resection or exclusion of small bowel, low blood and urine xylose levels occur. With successful treatment of these conditions, the test becomes normal. In chronic renal disease, nephrosis and myx-edema, high blood and low urine xylose levels probably result from decreased glomerular filtration rate and depression of renal xylose excretion. The test is not changed significantly in normal subjects receiving adrenocortlcal steroid therapy; in simple diarrhea; in all forms of secondary steatorrhea not due to diffuse small bowel pathology; in acute and chronic liver disease with or without ascites; in acute renal disease; in partial gastectomy with or without steatorrhea; in macrocytic anemia and in hyperthyroidism. Clinically, abnormalities in the test appear to result from only 2 important factors: defective intestinal absorption and defective glomerular filtration.