D-xylose absorption test

Evaluates carbohydrate absorption by the proximal small intestine. Indications: - diagnosis of malabsorption Contraindications: - useless in anephric patients Normal values: 1) adult a) serum 1] 25 g dose: > 25 mg/dL 2] 5 g dose: > 20 mg/dL b) urine 1] 25 g dose: > 4.0 g/hour (> 3.5 g/hour if > 65 years) 2] 5 g dose: > 1.2 g/hour 2) children a) serum: > 30 mg/dL b) urine: 16-33% of ingested dose Increases: - alcohol Decreases: 1) intestinal malabsorption of carbohydrates - normal in pancreatic insufficiency 2) bacterial overgrowth in the small intestine 3) vomiting 4) ascites 5) delayed gastric emptying 6) Whipple's disease 7) urine levels may be decreased with: a) renal insufficiency b) hypothyroidism 8) pharmaceutical agents a) aminosalicylic acid b) arsenicals c) colchicine d) digitalis e) ethionamide f) gold g) indomethacin h) isocarboxazid i) kanamycin j) MAO inhibitors k) metformin l) nalidixic acid m) neomycin n) opium alkaloids o) phenelzine p) phenformin q) atropine Procedure: 1) adults: a) 25 g oral dose of D-xylose (in 250 mL of water) b) 5 g oral dose may cause less gastrointestinal disturbance but the test is less sensitive c) D-xylose is measured in serum 2 hours later d) urine is collected for 5 hours 2) children a) 0.5 g/kg orally as 5% solution (maximum 25 g) b) D-xylose is measured in serum 1 hours later c) urine is collected for 5 hours Specimen: 1) whole blood (NaF/oxalate) 2) urine 5 hour; collect in dark, refrigerated bottle * validity of the test is enhanced if blood & urine measurements are performed simultaneously to rule out renal retention; in patients with renal insufficiency use serum levels only

Related

malabsorption xylose

References

Clinical Guide to Laboratory Tests, 3rd edition, NW Tietz ed, WB Saunders, Philadelphia, 1995