Overview
The D Xylose Absorption Test is a diagnostic procedure and important absorption test used in the gastrointestinal workup of Malabsorption. It evaluates the ability of the proximal jejunum to absorb D-xylose, a pentose sugar absorbed by passive diffusion independent of pancreatic enzymes. After administering a 25-gram dose, D-xylose levels are measured via blood sample at one-hour level and two-hour level, along with five-hour excretion through urine collection. Since D-xylose undergoes minimal metabolism, low absorption directly reflects impaired intestinal mucosa and loss of mucosal integrity. The test serves as a differentiation test to distinguish mucosal disease from pancreatic insufficiency. Its clinical utility has historical significance (historical use), although modern alternatives such as serology, tTG-IgA, fecal elastase, and duodenal biopsy are now preferred in many settings due to certain limitations.
Symptoms
The D Xylose Absorption Test is indicated in patients with suspected Malabsorption presenting with chronic diarrhea, bulky or greasy stools, unintentional weight loss, abdominal distension, fatigue, and nutritional deficiencies. Additional findings may include anemia, bone pain, muscle weakness, and delayed growth in children. Persistent gastrointestinal complaints despite treatment necessitate a structured gastrointestinal workup, where this test helps identify low absorption versus normal absorption patterns.
Causes
Abnormal results in the D Xylose Absorption Test arise from impaired absorption across the intestinal mucosa. Reduced blood and urine D-xylose indicate mucosal disease such as celiac disease, Crohn’s Disease, and Whipple’s disease. In contrast, normal absorption of D-xylose with ongoing malabsorption suggests pancreatic insufficiency, where digestive failure is due to lack of pancreatic enzymes. Interpretation must consider normal values based on one-hour level, two-hour level, and five-hour excretion. False-positive results may occur in renal impairment, while false-negative results may be seen with delayed gastric emptying or improper urine collection.
Risk Factors
Risk factors for abnormal results include chronic inflammatory conditions affecting the intestinal mucosa, including celiac disease, Crohn’s Disease, and infections such as Whipple’s disease. Factors interfering with test accuracy include renal impairment, severe dehydration, delayed gastric emptying, and bacterial overgrowth. Recent drug intake, especially antibiotics, may alter intestinal flora and absorption patterns. Improper fasting or incomplete urine collection also contribute to misleading results.
Prevention
