Type of test Blood; urine
Normal findings
Test explanation and related physiology
d-Xylose is a monosaccharide that is easily absorbed by the normal intestine. In patients with malabsorption, intestinal d-xylose absorption is diminished; as a result, blood levels and urine excretion are reduced. d-Xylose is the monosaccharide chosen for the test because it is not metabolized by the body. Its serum levels directly reflect intestinal absorption.
This particular monosaccharide does not require pancreatic or biliary exocrine function. Its absorption is directly determined by the small intestine. This test is used to separate patients with diarrhea caused by maldigestion (pancreatic or biliary dysfunction) from those with diarrhea caused by malabsorption (sprue, Whipple disease, Crohn disease).
In this test, the patient is asked to drink a fluid containing a prescribed amount of d-xylose. Blood and urine levels are subsequently evaluated. Excellent gastrointestinal absorption is documented by high blood levels and good urine secretion of d-xylose. Poor intestinal absorption is marked by decreased blood levels and urine excretion.
Contraindications
• Patients with abnormal kidney function
• Patients who are dehydrated
Interfering factors
* Drugs that may affect test results include aspirin, atropine, and indomethacin.
Procedure and patient care
Before
* Explain the procedure to the patient.
* Instruct the adult patient to fast for 8 hours before testing.
* Tell the pediatric patient or the parents that the patient should fast for at least 4 hours before testing.
During
• Collect a venous blood sample in a red-top tube before the patient ingests the d-xylose.
• Collect a first-voided morning urine specimen and send it to the laboratory.
• Ask the patient to drink the prescribed dose of d-xylose dis solved in 8 oz of water. Record the time of ingestion.
• Calibrate pediatric doses according to body weight.
• Repeat venipunctures to obtain blood in exactly 2 hours for an adult and 1 hour for a child.
• Collect urine for a designated time, usually 5 hours. Refrigerate the urine during the collection period.
• Observe the patient for nausea, vomiting, and diarrhea, which may occur as side effects of d-xylose.
* Instruct the patient to remain in a restful position. Intense physical activity may alter digestion and affect results.
After
• Apply pressure to the venipuncture site.
* Inform the patient that normal activity may be resumed after completion of the study.
Abnormal findings
Decreased levels
- Sprue
- Lymphatic obstruction
- Enteropathy (e.g., radiation)
- Crohn disease
- Whipple disease
- Small intestine bacterial overgrowth
- Hookworm
- Viral gastroenteritis
- Giardia lamblia infestation
- Short-bowel syndrome
