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Disease Categories > Gastrointestinal Disease

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Malabsorption

Malabsorption is characterized by the inability to digest or absorb nutrients from the small intestine into the bloodstream and is related to diseases of the pancreas, liver or intestine.

Pathophysiology

Nutrient digestion and absorption occurs in three phases
- Luminal phase – breakdown and solubilization of proteins, carbohydrates, and fats by digestive enzymes and bile
- Mucosal phase – transport of digested nutrients into gastrointestinal epithelial cells
- Transport phase – transport of nutrients via lymphatics and portal circulation from small intestine to other parts of the body
Any process that disrupts one or more of these phases can cause malabsorption
Causes of malabsorption include:
- Inadequate digestion of nutrients
  - Deficiencies of pancreatic enzymes (eg, chronic pancreatitis, carcinoma of pancreas, cystic fibrosis).
  - Impaired synthesis or secretion of bile (eg, biliary obstruction, cirrhosis)
  - Deconjugation of bile salts (eg, blind-loop syndrome)
- Inadequate absorption of nutrients
  - Shortened bowel or loss of absorptive surface (eg, ulcerative colitis, Crohn disease, gluten-sensitive enteropathy [Celiac sprue], tropical sprue, lymphoma, surgical loss of functional bowel, blind-loop syndrome and hormonal disorders)
  - Impaired nutrient metabolism (eg, deficiency of intestinal disaccharidases)
  - Nutrient-specific transport deficiencies (eg, Hartnup disease)
  - Decreased availability of specific nutrients (eg, decreased vitamin B12 due to decreased intrinsic factor)

Laboratory Testing

Refer to the Malabsorption Testing algorithm

Indications for Ordering

Tests generally appear in the order most useful for common clinical situations
Click on number for test-specific information in the ARUP Laboratory Test Directory

Test Name and Number	Recommended Use	Limitations	Follow Up
Fat, Fecal Qualitative 0020385 Method: Microscopic/Stain/Heat	Determine presence of steatorrhea Determine etiology of malabsorption Increased neutral fats suggest a deficiency of pancreatic enzymes; increased split fats suggest impaired bile secretion or inadequate absorption of nutrients Include as part of metabolic or fat balance studies	Patient cannot be on a low-fat diet
Fat, Fecal Quantitative 0020386 Method: Gravimetric	Definitive test for determining the presence of malabsorption Include as part of metabolic or fat balance studies	Patient cannot be on a low-fat diet Quantitative test requires a 72-hour stool collection	If increased, consider xylose absorption test for assessment of intestinal mucosa integrity
Pancreatic Elastase, Fecal 0080526 Method: Enzyme-Linked Immunosorbent Assay	Evaluate exocrine pancreatic function Determine etiology of pancreatic insufficiency Sensitive and specific test for pancreatic insufficiency		If pancreatic insufficiency is present, consider cystic fibrosis testing
Disaccharidase Determination 0090597 Method: Spectrophotometer	Evaluate patients suffering with chronic diarrhea, intestinal upset, or failure to thrive
Lactose Tolerance 0020407 Method: Enzymatic	Evaluate mucosal absorption efficiency in a variety of malabsorptive diseases in children May be used for diagnosing lactose deficiency

Additional Tests Available

Click on number for test-specific information in the ARUP Laboratory Test Directory

Test Name and Number	Comments
Xylose Absorption Test (Adult - 25 g dose) 0020609 Method: Spectrophotometry	Decreased absorption of D-xylose is due to impaired intestinal absorption
Xylose Absorption Test (Child) 0020612 Method: Spectrophotometry
Xylose Absorption Test (Adult - 5g dose) 0020615 Method: Spectrophotometry	The 5g dose is preferred in patients who do not tolerate the 25g dose
Fat, Fecal Quantitative 24-Hour Collection (Includes Homogenization) 0060724 Method: Gravimetric
Fat, Fecal Quantitative 48-Hour Collection (Includes Homogenization) 0060748 Method: Gravimetric
Fat, Fecal Quantitative 72-Hour Collection (Includes Homogenization) 0060772 Method: Gravimetric

Additional Information

The xylose absorption tests evaluate carbohydrate absorption by the mucosa of the proximal small intestine. In patients with renal deficiency, rely on the serum test only. In functionally anephric patients, the test is unreliable. Nonfasting serum samples are often compromised by significant analytic interferences.