Description
Xylose is a 5-carbon monosaccharide (a type of sugar) that is absorbed from the proximal small intestine following digestion by pancreatic enzymes. The rate of absorption is measured by taking blood samples at regular intervals after oral administration.

This test cannot be used for cats because of insensitivity and wide individual variation in xylose absorption in this species.

Method
The patient must be fasted for 12 hours before the test. A fixed amount of xylose (500mg/kg as a 10-25% solution) is introduced directly into the stomach by gastric intubation (e.g. via a nasogastric tube). Blood samples are taken from the patient before the xylose is given and at hourly intervals afterwards for 5 hours. The concentration of D-Xylose in the blood samples is determined by standard laboratory techniques.

Results

Normal dogs - After 1 hour the mean concentration is 63mg/dl +/- 12.

Plasma concentrations above 50mg/dl are normal

Plasma concentrations between 45 and 50 mg/dl are inconclusive, but above 45mg/dl after 90 minutes is normal.

Dogs with malabsorption have plasma xylose concentrations of 13-43 mg/dl after 90 minutes.

Other causes of delayed xylose absorption include: