Malabsorption

Background
Dx
Lab Tests
Algorithm

Diagnostic Algorithm

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 or intestine.

Causes of Malabsorption

Inadequate digestion of nutrients
- Deficiencies of pancreatic enzymes (eg, chronic pancreatitis, pancreatic carcinoma, 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, 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
- Amyloidosis, systemic sclerosis (scleroderma), hyperthyroidism, Zollinger-Ellison syndrome, atrophic gastritis, medication-induced malabsorption, neurofibromatosis

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

Diagnosis

Indications for Testing

Diarrhea, steatorrhea, 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
- Fecal tests – perform in parallel with serum tests
  - Fecal fat, qualitative/quantitative
  - Stool culture, ova and parasite – rule out infectious diarrhea
  - Fecal leukocytes – present in IBD, infectious diarrhea
  - Fecal occult blood or guaiac
- Consider celiac serologies
- If initial test results are abnormal, proceed to testing based on suspected disease (see the Malabsorption Testing Algorithm)
- If initial test results are normal, consider other tests – abdominal CT or ultrasound, endoscopy

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: Ion-Selective Electrode/Enzymatic	Assess for inflammatory processes
Sedimentation Rate, Westergren (ESR) 0040325 Method: Westergren	Assess for inflammatory processes
Aspartate Aminotransferase, Serum or Plasma 0020007 Method: Enzymatic	Screen for other causes of malabsorption
Alanine Aminotransferase, Serum or Plasma 0020008 Method: Enzymatic	Screen for other causes of malabsorption
Albumin, Serum by Nephelometry 0050671 Method: Nephelometry	Assess nutritional status
Thyroid Stimulating Hormone 0070145 Method: Electrochemiluminescent Immunoassay	Rule out thyroid disease as cause for malabsorption
Occult Blood, Fecal 0020374 Method: Colorimetry	Assess for fecal blood
Lactoferrin, Fecal by ELISA 0061164 Method: Enzyme-Linked Immunosorbent Assay	Assess bowel inflammation Determine presence of fecal leucocytes
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	Results can not be used if patient on low fat diet
Ova & Parasite Exam, Fecal (Immunocompromised or Travel History) 2002272 Method: Concentration Technique/Trichrome Stain/Microscopic Evaluation	Rule out parasites as cause for malabsorption in immunocompromised patients and patients with appropriate travel history
Celiac Disease Reflexive Panel 0051065 Method: Nephelometry/Enzyme-Linked Immunosorbent Assay	Rule out celiac disease
Immunoglobulin A, Serum 0050340 Method: Nephelometry	Rule out celiac disease
Tissue Transglutaminase Antibody, IgG 0056009 Method: Enzyme-Linked Immunosorbent Assay	Rule out celiac disease
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
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
Xylose Absorption Test (Adult - 5g dose) 0020615 Method: Spectrophotometry	Evaluate carbohydrate absorption by the mucosa of the proximal small intestine The 5g dose is preferred in patients who do not tolerate the 25g dose
Xylose Absorption Test (Adult - 25 g dose) 0020609 Method: 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: Spectrophotometry	Evaluate carbohydrate absorption by the mucosa of the proximal small intestine
Lactose Tolerance 0020407 Method: 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 Number	Comments
Disaccharidase, Tissue 2002247 Method: 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: Freezing Point Depression
Fat, Fecal Quantitative 72-Hour Collection (Includes Homogenization) 2002356 Method: Nuclear Magnetic Resonance Spectroscopy
Carotenes, Fractionated, Plasma or Serum 0021021 Method: High Performance Liquid Chromatography
Electrolytes, Fecal 0060185 Method: Ion-Selective Electrode
pH, Fecal 0020518 Method: pH Indicator Strips or pH meter
Reducing Substances, Fecal 0020373 Method: Colorimetry
Trypsin-Like Immunoreactivity 0070003 Method: Radioimmunoassay
Carotene, Serum Total 0080055 Method: Spectrophotometry