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A. Diseases Associated with Malabsorption

  1. Diabetes Mellitus
  2. Celiac Disease
  3. Inflammatory Bowel Disease (IBD)
  4. Infections
    1. Human Immunodeficiency Virus
    2. Giardiasis
    3. Whipple's Disease
    4. Tropical Sprue (likely infectious)
  5. Mesenteric or Gastric Ischemia [6]
  6. Bile Salt Malabsorption
  7. Pernicious Anemia
  8. Short Gut Syndromes
    1. Usually associated with surgery
    2. Bacterial overgrowth
  9. Systemic Sclerosis
  10. Primary Systemic Amyloidosis [5]
  11. Lactase Deficiency

B. Mechanisms of Malabsorption
[Figure] "Evaluation of Diarrhea"

  1. Emulsification
    1. Loss of gastric churning
    2. Post-gastrectomy
    3. Gastrojejunostomy
  2. Cholecystekinin (CCK) - Pancreazymin (PZ) Release
    1. CCK and PZ are the same hormone
    2. Stimulate Gall bladder emptying and pancreatic digestive enzyme release
    3. Duodenum has highest amount of CCK-PZ and secretin producing cells
    4. Bypass of duodenum by gastrojejunostomy decreases CCK-PZ
  3. Pancreatic Lipolysis
    1. Exocrine pancreatic insufficiency from any cause
    2. Low duodenal pH will destroy enzyme (eg. extreme acid, ZE syndrome gastrinoma)
  4. Bile Acid Insufficiency, Inadequate Micelle Formation
    1. Bile acid required, decreased in various liver disease and bile duct obstruction
    2. Precipitation of bile salts from intestinal lumen by low pH, drugs (cholestyramine)
    3. Deconjugation of bile acids by overgrowth of intestinal bacteria (lactase deficiency)
  5. Chylomicron Transport
    1. Failure to synthesize protein coat of chylomicrons leads to decreased export of lipid
    2. Disease is called ß-Lipoproteinemia
    3. Associated red blood cell membrane abnormalities
  6. Lymphatic Transport
    1. Blockage of lymphatic drainage by tumor or infection
    2. Especially in Whipple's disease (intestinal / villous lymphatic blockade)
    3. Intestinal lymphangiectasis = developmental hypoplasia of lymphatics
  7. Short Bowel Syndrome
    1. In children, usually due to congenital malformations requiring surgical resection
    2. In adults, usually follows major abdominal surgery with intestinal resection
    3. Diarrhea, weight loss, fatigue very common
    4. D-lactate acidosis may be associated with short bowel syndrome [3]
    5. Growth hormone, glutamine, and modified diet of some efficacy [4]

C. Symptoms and Signs of Malabsorption

  1. Weight Loss due to inadequate caloric absorption
  2. Steatorrhea: fat malabsorption
  3. Diarrhea: inadequate Hydroxylated fatty acids
  4. Bloating: formation of methane, H2, water with inadequate absorption
  5. Anemia: Iron, Folate or Vitamin B12 malabsorption
  6. Edema: inadequate protein in blood leads to reduced oncotic pressure
  7. Tetany: Calcium and Magnesium malabsorption
  8. Osteoporosis
    1. Calcium Deficiency
    2. Protein
    3. Vitamin D - deficiency can also lead to osteomalacia [2]
  9. Milk (Lactose) Intolerance
    1. Very common
    2. Leads to bacterial colonization in small intestinal
  10. Bleeding and Bruising: Vitamin K malabsorption

D. Laboratory Findings

  1. Hypoalbuminemia: caused by:
    1. Liver Failure (failed synthesis
    2. Nephrotic Syndrome (loss in urine)
    3. Malabsorption (protein losing enteropathy)
  2. Hypocalcemia
    1. Renal Failure
    2. Medullary thyroid carcinoma
    3. Parathyroid insufficiency
  3. Prolonged Prothrombin Time usually associated with hepatic insufficiency
  4. Reduced Carotene Level
  5. Abnormal small bowel radiographic tests
  6. Steatorrhea: Sudan Black stain of stool
  7. Increased fat in 72 hour fecal fat collection
  8. Amyloidosis needs to be considered, as prognosis is very poor [5]

E. Specific Tests

  1. D-xylose test:
    1. Evaluates overall absorptive capacity
    2. Give xylose, normally excreted ~6 hours later in urine
    3. In malabsorption, this is not absorbed, not found in urine
  2. Small Bowel Radiograph
    1. Normal folds and loops most common
    2. Dilations, increased folds may also occur
  3. Jejunal Biopsy
    1. Diagnostic: Whipple's Disease, AB lipoproteinemia, Amyloidosis, Giardia
    2. Characteristic: Celiac Disease, Sprue, Crohn's Disease, Eosinophilic gastroenteritis
    3. Non-specific: pancreatic insufficiency, bile salt deficiency, bacteria in lumen
  4. 14C-Glycocholate: Conversion to 14-CO2 by bacteria
  5. Schilling Test [1]
    1. Vitamin B12 Absorption test is done in two parts
    2. In part 1, the patient is given vitamin B12 alone and urinary excretion measured
    3. In part 2, the patient is given vitamin B12 with intrinsic factor, and urine B12 measured
    4. Patients with normal intrinsic factor have a normal part 1
    5. Patients who do not make intrinsic factor have a normal part 2
    6. Patients who cannot bind B12-intrinsic factor complex have abnormal parts 1 and 2
    7. Since this complex binds in the terminal ileum, abnormalities there may be documented
    8. Most common causes of terminal ileal diseases are Crohns and Short Bowel Syndrome
  6. Bentiromide Test
    1. Pancreatic function test
    2. Adequate duodenal chymotrypsin necessary to cleave PABA from substrate
    3. Give 500mg dose bentiromide, absorbed in duodenum, to liver, to urine
    4. Measure level in 6 hour urine sample
    5. Pancreatic enzyme output must be <5% of normal for urinary PABA to decrease

Resources

calcCoefficient of Fat Absorption

References

  1. Toh BH, van Driel KR, Gleeson PA. 1997. NEJM. 337(20):1441 abstract
  2. Basha B, Rao S, Han ZH, et al. 2000. Am J Med. 108(4):296 abstract
  3. Gavazzi C, Stacchiotti S, Cavalletti R, Lodi R. 2001. Lancet. 357(9265):1410 (Case Report)
  4. Byrne TA, Persinger RL, Young LS, et al. 1995. Ann Surg. 222:243 abstract
  5. Hayman SR, Lacy MQ, Kyle RA, Gertz MA. 2001. Am J Med. 111(7):535 abstract
  6. Haberer J, Trivedi NN, Kohlwes J, Tierney L Jr. 2003. NEJM. 349(1):73 (Case Discussion) abstract