Malabsorption

Diagnosis

Indications for Testing

  • Diarrhea, steatorrhea, or preexisting condition that may predispose to malabsorption

Laboratory Testing

  • Initial screening tests
    • CBC
      • Mild anemia frequent; leukocytosis in IBD or infectious etiology
      • Eosinophilia – consider parasitic evaluation
    • Electrolyte panel
    • ESR – elevated in inflammatory or infectious processes
    • Liver enzymes, including albumin – low albumin suggests chronic processes
    • TSH – rule out thyroid disease
    • In children and adolescents – cystic fibrosis testing (sweat chloride)
    • Fecal tests – perform in parallel with serum tests
      • Stool culture, ova and parasite – rule out infectious diarrhea (bacterial, viral, parasitic); C. difficile testing if risk factors present
      • Fecal leukocytes – present in IBD, infectious diarrhea
      • Fecal occult blood
      • Fecal fat, qualitative/quantitative
    • Consider celiac serologies (tTG antibody testing with IgA level)
    • If initial test results are abnormal, proceed to testing based on suspected disease (see the Malabsorption Testing Algorithm)
  • Secondary testing – hydrogen breath test; serum or urine D-xylose; vitamins A, D, E, B12; pancreatic enzyme analysis

Imaging Studies

  • If initial test results are normal, consider abdominal CT or ultrasound, endoscopy

Differential Diagnosis

  • See causes of malabsorption in Clinical Background

Clinical Background

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, and intestine.

Causes of Malabsorption

  • Inadequate digestion of nutrients
  • Inadequate absorption of nutrients
    • Shortened bowel or loss of absorptive surface (eg, inflammatory bowel disease [IBD], including ulcerative colitis, Crohn disease, gluten-sensitive enteropathy [Celiac sprue], tropical sprue, lymphoma, surgical loss of functional bowel, blind-loop syndrome, hormonal disorders)
    • Impaired nutrient metabolism (eg, deficiency of intestinal disaccharidases, lactase deficiency)
    • Nutrient-specific transport deficiencies (eg, Hartnup disease)
    • Decreased availability of specific nutrients (eg, vitamin B12 deficiency due to decreased intrinsic factor)
    • Alterations of circulation (eg, mesenteric ischemia, heart failure, portal hypertension, lymphatic obstruction
  • Miscellaneous

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

Clinical Presentation

  • Prominent symptom – diarrhea
  • Constitutional – weight loss, fatigue
  • Gastrointestinal – steatorrhea, abdominal bloating, abdominal pain, somatostatinoma
  • Extraintestinal – anemia, skin rashes, stomatitis, glossitis, peripheral edema, ascites

Indications for Laboratory Testing

  • 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
CBC with Platelet Count 0040002
Method: Automated Cell Count

Assess for presence of anemia and leukocytosis

   
Electrolyte Panel 0020410
Method: Quantitative Ion-Selective Electrode/Enzymatic

Assess for inflammatory processes 

   
Sedimentation Rate, Westergren (ESR) 0040325
Method: Visual Identification

Assess for inflammatory processes

Elevated in inflammatory or infectious processes

   
Aspartate Aminotransferase, Serum or Plasma 0020007
Method: Quantitative Enzymatic

Screen for other causes of malabsorption

   
Alanine Aminotransferase, Serum or Plasma 0020008
Method: Quantitative Enzymatic

Screen for other causes of malabsorption

   
Albumin by Nephelometry 0050671
Method: Quantitative Nephelometry

Assess nutritional status 

Low albumin suggestive of chronic process

   
Thyroid Stimulating Hormone with reflex to Free Thyroxine 2006108
Method: Quantitative Electrochemiluminescent Immunoassay

Rule out thyroid disease as cause for malabsorption

   
Occult Blood, Fecal by Immunoassay 2007190
Method: Quantitative Immunoassay

Assess for fecal blood 

   
Lactoferrin, Fecal by ELISA 0061164
Method: Qualitative Enzyme-Linked Immunosorbent Assay

Assess bowel inflammation

Determine presence of fecal leukocytes 

   
Fat, Fecal Qualitative 0020385
Method: Qualitative Microscopy/Stain

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

Results can not be used if patient on low fat diet

 
Fat, Fecal Quantitative, Homogenized Aliquot 2002350
Method: Nuclear Magnetic Resonance Spectroscopy

Definitive test for determining the presence of malabsorption

Include as part of metabolic or fat balance studies

Results cannot be used if patient on low-fat diet

Quantitative test requires a 72-hour stool collection

If increased, consider xylose absorption test for assessment of intestinal mucosa integrity

Ova & Parasite Exam, Fecal (Immunocompromised or Travel History) 2002272
Method: Qualitative Concentration/Trichrome Stain/Microscopy

If parasite infection is suspected as cause of persistent diarrhea (>5 to 7 days), specific pathogen testing is recommended (eg, Giardia antigen by EIA)

Do not order for patients who develop diarrhea during a prolonged hospitalization

Stool antigen testing is the optimal test method for determining the parasitic presence of Giardia duodenalis (synonyms Giardia lamblia, Giardia intestinalis), Cryptosporidium spp, or Entamoeba histolytica

The ova and parasite exam does not specifically detect Cryptosporidium, Cyclospora, Isospora, and Microsporidia; for Cryptosporidium, refer to the Cryptosporidium Antigen by EIA test; for Cyclospora and Isospora, refer to Parasitology Stain by Modified Acid-Fast; for Microsporidia, refer to Microsporidia Stain

 
Celiac Disease Reflexive Cascade 2008114
Method: Quantitative Nephelometry/Semi-Quantitative Enzyme-Linked Immunosorbent Assay//Semi-Quantitative Indirect Fluorescent Antibody

Rule out celiac disease

   
Immunoglobulin A 0050340
Method: Quantitative Nephelometry

Rule out celiac disease

   
Tissue Transglutaminase Antibody, IgG 0056009
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Rule out celiac disease

   
Pancreatic Elastase, Fecal 0080526
Method: Quantitative 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

Xylose Absorption Test (Adult - 5g dose) 0020615
Method: Quantitative Spectrophotometry

Evaluate carbohydrate absorption by the mucosa of the proximal small intestine

5g dose is preferred in patients who do not tolerate the 25g dose

   
Xylose Absorption Test (Adult - 25g dose) 0020609
Method: Quantitative Spectrophotometry

Evaluate carbohydrate absorption by the mucosa of the proximal small intestine

Decreased absorption of D-xylose is due to impaired intestinal absorption

   
Xylose Absorption Test (Child) 0020612
Method: Quantitative Spectrophotometry

Evaluate carbohydrate absorption by the mucosa of the proximal small intestine

   
Lactose Tolerance 0020407
Method: Quantitative Enzymatic

Evaluate mucosal absorption efficiency in a variety of malabsorptive diseases in children

May be used for diagnosing lactose deficiency

Components include fasting glucose, 30-minute glucose, 1-hour glucose, 2-hour glucose-LACTOL, 3-hour glucose

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Thyroid Stimulating Hormone 0070145
Method: Quantitative Chemiluminescent Immunoassay
Disaccharidase, Tissue 2002247
Method: Quantitative Spectrophotometry

Evaluate patients suffering with chronic diarrhea, intestinal upset, or failure to thrive

Fat, Fecal Quantitative 24-Hour Collection (Includes Homogenization) 2002354
Method: Nuclear Magnetic Resonance Spectroscopy
Fat, Fecal Quantitative 48-Hour Collection (Includes Homogenization) 2002355
Method: Nuclear Magnetic Resonance Spectroscopy
Osmolality, Fecal 0098122
Method: Quantitative Freezing Point
Fat, Fecal Quantitative 72-Hour Collection (Includes Homogenization) 2002356
Method: Nuclear Magnetic Resonance Spectroscopy
Carotenes, Fractionated, Plasma or Serum 0021021
Method: Quantitative High Performance Liquid Chromatography
Electrolytes, Fecal 0060185
Method: Quantitative Ion-Selective Electrode
pH, Fecal 0020518
Method: Quantitative pH Indicator Strips/Quantitative pH Meter
Reducing Substances, Fecal 0020373
Method: Semi-quantitative Colorimetry
Trypsin-Like Immunoreactivity 0070003
Method: Quantitative Radioimmunoassay

Results should be correlated with clinical presentation and other diagnostic data for the diagnosis of pancreatitis

Carotene, Serum Total 0080055
Method: Quantitative Spectrophotometry
Hepatic Function Panel 0020416
Method: Quantitative Enzymatic/Quantitative Spectrophotometry

Initial screening test for hepatobiliary problems

Panel includes albumin; ALP; AST; ALT; bilirubin, direct; protein, total; and bilirubin, total

Vitamin A (Retinol), Serum or Plasma 0080525
Method: Quantitative High Performance Liquid Chromatography
Vitamin D, 25-Hydroxy 0080379
Method: Quantitative Chemiluminescent Immunoassay

Preferred screening test for vitamin D deficiency

Preferred test to monitor response to supplementation

Vitamin E, Serum or Plasma 0080521
Method: Quantitative High Performance Liquid Chromatography
Vitamin B12  0070150
Method: Quantitative Chemiluminescent Immunoassay
Clostridium difficile toxin B gene (tcdB) by PCR 2002838
Method: Qualitative Polymerase Chain Reaction