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Definition

What is d-xylose absorption test?

The D-xylose absorption test measures the level of D-xylose (a type of sugar) in your blood or urine. This examination is done to diagnose problems that prevent the small intestine from absorbing nutrients from food. D-xylose is generally easily absorbed by the intestines. When absorption problems arise, D-xylose is not absorbed by the intestines, and its levels in the blood or urine will decrease.

When should I take the d-xylose absorption test?

If your intestines are unable to properly absorb D-xylose, your doctor will arrange for this series of tests to determine if you have malabsorption syndrome. This syndrome is caused when your small intestine — which is responsible for most of the digestion of food — is unable to absorb enough nutrients from your daily diet. Malabsorption syndrome can cause several symptoms, such as weight loss, chronic diarrhea, and a feeling of extreme weakness and fatigue.

Precautions & warnings

What should I know before taking the d-xylose absorption test?

If you have an abnormally high amount of bacteria in your intestines, you may need to take antibiotics for 1-2 days before testing. This series of tests can cause dehydration. Make sure you drink enough fluids to replace the fluids lost during the test. Tell your doctor if you have any concerns about diarrhea after taking the D-xylose solution. D-xylose levels in the blood are generally considered more reliable than using urine samples in children under 12 years of age.

A test that looks at the walls of the small intestine (upper digestive tract) may be used if your doctor suspects signs of Crohn's disease or other malabsorption syndromes.

Process

What should I do before undergoing the d-xylose absorption test?

You will be asked to fast foods containing pentose for 24 hours before running a series of tests. Pentose is a type of sugar similar to D-xylose. Pentose-rich foods include pastries, jellies, spread spreads and fruit. Your doctor may advise you to temporarily stop some medicines before running the test, because certain drugs will affect the test results. You are not allowed to eat or drink anything except plain water for 8-12 hours before the blood sample test. Children should avoid eating or drinking anything other than plain water for 4 hours before the test.

How is the d-xylose absorption test process?

The amount of D-xylose in urine and blood samples is measured before and after you drink the D-xylose solution. To start the test, your doctor will collect the first batch of samples of your blood and urine. Next, you will be given an oral D-xylose solution to drink. In adults, a blood sample is usually taken 1 hour after you drink the solution. Then, the next batch of blood samples will be taken 5 hours after you drink the D-xylose solution. You will need to collect all the urine you produce after 5 hours of drinking the D-xylose solution. Sometimes, urine will be collected after 24 hours from consumption of the solution.

Blood test

The medical personnel in charge of drawing your blood will take the following steps:

• wrap an elastic belt around your upper arm to stop blood flow. This makes the blood vessel under the bundle enlarge making it easier to insert the needle into the vessel
• clean the area to be injected with alcohol
• inject a needle into a vein. More than one needle may be required.
• Insert the tube into the syringe to fill it with blood
• untie the knot from your arm when enough blood is drawn
• attaching gauze or cotton to the injection site, after the injection is complete
• apply pressure to the area and then put a bandage on

Urine test

You will start collecting your urine from the morning. The first time you wake up in the morning, please pee, but do not include this urine in the urine sample that you will be submitting to the doctor. Note the exact time you urinate to mark the first 5 hours of the sample collection period.

In the next 5 hours, collect your urine again. Your medic or doctor will provide you with a large container that can hold about 4 liters of fluid. The container has a certain amount of preservative in it. Urinate into a small, sterilized container and pour your urine into a larger container. Do not touch the inside of the container with your fingers. Store large containers in the refrigerator during the sample collection period. Empty your bladder at the last time of collection or just before you end the 5 hour sample collection period. Try not to contaminate the container with foreign objects, such as tissues, pubic hair, feces, menstrual blood, and others.

You are not allowed to eat until the test is over.

What should I do after taking the d-xylose absorption test?

If your doctor suspects you have malabsorption syndrome, he or she will recommend a test to examine the walls of your small intestine. If you have intestinal parasites, your doctor will schedule additional tests to determine the type of parasite and the appropriate therapy for your condition.

If your doctor suspects that you have short bowel syndrome, he or she will recommend changing your diet or prescribing medication.

Explanation of the Test Results

What do my test results mean?

D-xylose levels in the blood reach their highest level within 2 hours of drinking the D-xylose solution. Most of the D-xylose will be washed away in the urine during the first 5 hours. If your intestines can't absorb D-xylose properly, the amount of D-xylose in the blood and urine will be very low.

Certain conditions can change D-xylose levels. Your doctor will discuss any abnormal results that appear significant with you in relation to your signs and your medical history.

Normal

Depending on the laboratory of your choice, the normal range of this test may vary. Discuss any questions you have about your medical test results with your doctor.

D-xylose in datah
Infants (5-gram dose):	More than 15 milligrams per deciliter (mg / dL) or more than 1.0 millimole per liter (mmol / L)
Children (5-gram dose):	More than 20 mg / dL or more than 1.3 mmol / L
Adults (5-gram dose):	More than 20 mg / dL in 2 or more than 1.3 mmol / L
Adults (25-gram dose):	More than 25 mg / dL in 2 or more than 1.6 mmol / L

D-xylose in urine (5 hour urine sample)
Children:	16% –33% D-xylose is found
Adult:	More than 16% D-xylose is found or greater than 4 grams (g) was found
Adults 65 and older:	More than 14% of the D-xylose dose or more than 3.5 found

Low levels

Low levels are caused by:

• diseases that affect the ability of the intestines to absorb nutrients (malabsorption syndrome), such as celiac disease, Crohn's disease, or Whipple's disease
• inflammation of the intestinal wall
• short bowel syndrome
• parasitic infections, for example glardiasis or hookworm
• an infection that causes vomiting (food poisoning or flu)