Xylose tolerance test; Diarrhea - xylose; Malnutrition - xylose; Sprue - xylose; Celiac - xylose
D-xylose absorption is a laboratory test to determine how well the intestines absorb a simple sugar (D-xylose). The test helps determine if nutrients are being properly absorbed.
The test requires a blood and urine sample. These tests include:
There are several ways to perform this test. A typical procedure is described below, but make sure you follow the specific instructions you are given.
You will be asked to drink 8 ounces (240 ml) of water that contains 25 grams of a sugar called d-xylose. The amount of d-xylose that comes out in your urine over the next 5 hours will be measured. You may have a blood sample collected at 1 and 3 hours after drinking the liquid. The amount of urine you produce over a 5-hour period is also determined. Your health care provider will tell you how to collect all of the urine during a 5-hour period.
How to Prepare for the Test
Do not eat or drink anything (even water) for 8 to 12 hours before the test. Do not exercise before the test. A failure to restrict activity may affect test results.
Your provider may tell you to stop taking certain drugs that can affect test results. Drugs that can affect test results include aspirin, atropine, indomethacin, isocarboxazid, and phenelzine. Never stop taking any medicine without first talking to your doctor.
How the Test will Feel
When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.
Urine is collected as part of normal urination with no discomfort.
Why the Test is Performed
Your provider may order this test if you have:
- Persistent diarrhea
- Signs of malnutrition
- Unexplained weight loss
This test is primarily used to determine if nutrient absorption problems are due to a disease of the intestines.
A normal result depends on how much D-xylose is given. In most cases, the test results are either positive or negative. A positive result means that D-xylose is found in the blood or urine and is therefore being absorbed by the intestines.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
Lower than normal values may be seen in:
Risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Multiple tests may be necessary to determine the reason for malabsorption.
Hogenauer C, Hammer HF. Maldigestion and malabsorption. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 104.
Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 140.