Page 39 - To keep a balance in disease specific intestinal insufficiency. Diagnostics and practical nutritional aspects - Nicolette Wierdsma

Diagnostic tests for malabsorption and maldigestion
the (putative) gold standard for quantifying intestinal energy losses (21, 22). But by assessing only the intestinal output, it is not a sensitive marker for intestinal absorption, since bomb calorimetry per se is not related to nutritional intake in the feces collection period.
D-xylose absorption test
The D-xylose test is an indicator of overall nutrient absorption. By oral 3 administration of the monosaccharide D-xylose, small intestinal absorption
can be quantified. D-xylose is transported across the intestinal epithelium
(jejunum) by a passive, carrier mediated pathway. The standard oral dose for
adults is 25 g of D-xylose. To measure intestinal absorption, the following three specimens can be used: breath, urine, or blood. Approximately 50% of an intravenous dose is recovered in the urine. Furthermore, breath tests with D-xylose as substrate, including the hydrogen, 13C-D-xylose, and 14C-D-xylose breath test, are all available. Breath tests are often used for diagnosing bacterial overgrowth, relying on breakdown of the non-absorbed sugars by intestinal flora. In healthy individuals, the usual lower reference limit of the 5 hour urine test is 4 g, using a standard dose of 25 g D-xylose. For the 1 hour blood test, the putative lower reference limit is 25 mg/dL (15, 23-27).
Assessment of (dys)motility
In clinical practice, manometry remains one of the most important investigational techniques for gastrointestinal (dys)motility, in particular for esophageal, gastroduodenal and anorectal disorders. Yet, scintigraphy still is the gold standard for assessment of gastric emptying in clinical practice, manometry and 13C breath tests being alternatives, mostly in research. Many other techniques are being used mainly in the context of scientific research of which only some may become incorporated in the diagnostic armamentarium (28, 29).
Assessment of (mal)assimilation
Assimilation, being defined as the process of transporting (chemical) nutrient particles into the body cells, is closely related to intestinal cell (enterocyte) mass. Intestinal mass may be an indicator of absorption, because reduction in mass equals loss of absorptive surface area. No other test, to our knowledge, than fasting citrulline is proposed in literature.
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