Xylose Testing

Xylose, also known as D-xylose, is a type of sugar (carbohydrate) that is normally easily absorbed by your intestines. A xylose test checks the level of xylose in both your blood and urine to see how well you absorb carbohydrates. Usually, your body digests in stages.

The proteins, fats, and carbohydrates in the food you eat are: Broken down in the stomach by acid and enzymes (proteins that speed up certain chemical reactions in your body); Broken down further in your small intestines by pancreatic enzymes and bile (liquid made in your liver to help digest fats); Absorbed into your intestines to be used or stored; If you don't have enough bile or pancreatic enzymes, the carbohydrates and other foods you eat can't be digested well. Lower-than-normal xylose levels can mean there is a problem with your body's ability to absorb nutrients. Xylose testing is no longer routinely ordered to check for malabsorption, and it may not be available everywhere.

This test may be ordered as a follow-up test to other tests, such as a fecal fat test.

Why this test is done

You may need this test if you have symptoms of a malabsorption disorder, which include:

• Chronic (long-lasting) diarrhea
• Abdominal (belly) pain
• Bloating (a feeling of fullness or swelling in your belly)
• Gas
• Weight loss for no known reason, or in children, not being able to gain weight

How to prepare

You will need to fast (not eat or drink) for eight hours before the test. Children younger than nine years old should fast for four hours before the test.

For 24 hours before the test, you must avoid foods high in a type of sugar known as pentose, which is similar to xylose. These foods include jams, pastries, and fruits.

Some medicines may affect your test results. You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Your provider will let you know if you need to do any other preparations.

Sample type

Blood Urine Stool

Other names for this test

xylose tolerance test, xylose absorption test, D-xylose tolerance test, D-xylose absorption test