D-Xylose Absorption Test

The D-xylose absorption test is a medical diagnostic tool used to assess the integrity and function of the small intestine, particularly in relation to carbohydrate absorption.

Purpose

The primary purpose of the D-xylose absorption test is to diagnose malabsorption disorders, such as celiac disease, Crohn's disease, and other conditions that affect the small intestine's ability to absorb nutrients.

Procedure

The test involves administering a dose of D-xylose, a sugar molecule, to the patient, usually orally. The patient is then asked to collect urine samples over a specified period, typically 5 hours. In some cases, blood samples may also be collected to measure the level of D-xylose in the bloodstream.

How it Works

D-xylose is a monosaccharide that is normally absorbed by the small intestine and then excreted in the urine. If the small intestine is functioning properly, the majority of the ingested D-xylose will be absorbed and appear in the urine within a few hours. However, if there is malabsorption or damage to the small intestine, less D-xylose will be absorbed, resulting in lower levels in the urine.

Interpretation of Results

The results of the D-xylose absorption test are interpreted based on the amount of D-xylose excreted in the urine over the specified collection period. A low level of D-xylose in the urine may indicate malabsorption or damage to the small intestine, while a normal level suggests that the small intestine is functioning properly.

Preparation and Contraindications

Prior to undergoing the D-xylose absorption test, patients are typically required to fast for several hours and avoid certain medications that may interfere with the test results. The test is generally considered safe, but it may be contraindicated in patients with severe kidney disease or those who are pregnant or breastfeeding.

Limitations and Alternatives

The D-xylose absorption test has some limitations, including the potential for false-negative results in patients with mild malabsorption or those with certain underlying medical conditions. Alternative diagnostic tests, such as endoscopy or imaging studies, may be used in conjunction with or instead of the D-xylose absorption test to evaluate small intestine function and diagnose malabsorption disorders.