This test measures the intestines' ability to absorb D-xylose, a simple sugar, as an indicator of whether nutrients are being properly absorbed.

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. An initial blood and urine sample are taken

You are given 25 grams of D-xylose in 8 ounces of water. Blood is collected after 2 hours, and sometimes again after 5 hours. Urine is re-tested after 8 hours. Urine excretion over a 5-hour period is also determined (all of the urine during 5 hours is collected).

Urine collection:

Collect a "clean-catch" ("midstream") urine sample. To obtain a clean-catch sample, men or boys should wipe clean the head of the penis. Women or girls need to wash the area between the lips of the vagina with soapy water and rinse well. As you start to urinate, allow a small amount to fall into the toilet bowl (this clears the urethra of contaminants). Then, in a clean container, catch about 1 to 2 ounces of urine and remove the container from the urine stream. Give the container to the health care provider or assistant.

Thoroughly wash the area around the urethra. Open a urine collection bag (a plastic bag with an adhesive paper on one end), and place it on your infant. For boys, the entire penis can be placed in the bag and the adhesive attached to the skin. For girls, the bag is placed over the labia. Place a diaper over the infant (bag and all).

Check your baby frequently and remove the bag after the infant has urinated into it. For active infants, this procedure may take a couple of attempts--lively infants can displace the bag. The urine is drained into a container for transport back to the health care provider.

Blood collection:

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Do not eat or drink anything (even water) for 8-12 hours before the test. Do not exercise before the test. Consult the health care provider about the need to stop taking drugs that can affect test results (see "special considerations").

If the collection is being taken from an infant, a couple of extra collection bags may be necessary.

When the needle is inserted to collect the blood, a stinging sensation or prick will be felt. After the blood has been drawn, the puncture site may throb for a few minutes, and may feel bruised for a day or two.

Urine is collected as part of normal urination with no discomfort.

This test may be performed to help evaluate cases of:

• persistent diarrhea
• unexplained weight loss
• suspected malnutrition
• general weakness

This test is especially useful in distinguishing nutrient absorption problems that are due to disease of the intestines from those due to disease of the pancreas.