Definition of D-xylose absorption:

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.

How the test is performed:

The test requires a blood and urine sample. For information on how these samples are obtained, see:

• Clean catch urine specimen
• Venipuncture (blood draw)

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 of water that contains 25 grams of a sugar called D-xylose. Two hours later, you will have a blood sample collected. You may also need to give blood again after 5 hours. Your urine sample is tested 8 hours later. 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 health care 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 doctor may order this test if you have:

• General weakness
• Persistent diarrhea
• Unexplained weight loss
• Signs of malnutrition

This test is especially useful in determining if nutrient absorption problems are due to a disease of the intestines or a disease of the pancreas.