|Classification and external resources|
Whipple's disease: Alcian blue with apparently eosin counterstain enlarged villus with many macrophages
Some prefer to classify malabsorption clinically into three basic categories:
- (1) selective, as seen in lactose malabsorption.
- (2) partial, as observed in a-Beta-lipoproteinaemia.
- (3) total as in coeliac disease.
The main purpose of the gastrointestinal tract is to digest and absorb nutrients (fat, carbohydrate, protein, and fiber), micronutrients (vitamins and trace minerals), water, and electrolytes. Digestion involves both mechanical and enzymatic breakdown of food. Mechanical processes include chewing, gastric churning, and the to-and-fro mixing in the small intestine. Enzymatic hydrolysis is initiated by intraluminal processes requiring gastric, pancreatic, and biliary secretions. The final products of digestion are absorbed through the intestinal epithelial cells.
Malabsorption constitutes the pathological interference with the normal physiological sequence of digestion (intraluminal process), absorption (mucosal process) and transport (postmucosal events) of nutrients.
- Mucosal damage (enteropathy)
- Congenital or acquired reduction in absorptive surface
- Defects of specific hydrolysis
- Defects of ion transport
- Pancreatic insufficiency
- Impaired enterohepatic circulation
||This section is in a list format that may be better presented using prose. (May 2012)|
|Due to infective agents|
|Due to structural defects|
|Due to surgical structural changes|
|Due to mucosal abnormality|
|Due to enzyme deficiencies|
|Due to digestive failure|
|Due to other systemic diseases affecting GI tract|
Clinical features 
They can occur in a variety of ways and features might give a clue to the underlying condition. Symptoms can be intestinal or extra-intestinal - the former predominates in severe malabsorption.
- Diarrhoea, often steatorrhoea, is the most common feature. Watery, diurnal and nocturnal, bulky, frequent stools are the clinical hallmark of overt malabsorption. It is due to impaired water, carbohydrate and electrolyte absorption or irritation from unabsorbed fatty acid. Latter also results in bloating, flatulence and abdominal discomfort. Cramping pain usually suggests obstructive intestinal segment e.g. in Crohn's disease, especially if it persists after defecation.
- Weight loss can be significant despite increased oral intake of nutrients.
- Growth retardation, failure to thrive, delayed puberty in children
- Swelling or oedema from loss of protein
- Anaemias, commonly from vitamin B12, folic acid and iron deficiency presenting as fatigue and weakness.
- Muscle cramp from decreased vitamin D, calcium absorption. Also lead to osteomalacia and osteoporosis
- Bleeding tendencies from vitamin K and other coagulation factor deficiencies.
There is no single, specific test for malabsorption. As for most medical conditions, investigation is guided by symptoms and signs. A range of different conditions can produce malabsorption and it is necessary to look for each of these specifically. Many tests have been advocated, and some, such as tests for pancreatic function are complex, vary between centers and have not been widely adopted. However, better tests have become available with greater ease of use, better sensitivity and specificity for the causative conditions. Tests are also needed to detect the systemic effects of deficiency of the malabsorbed nutrients (such as anaemia with vitamin B12 malabsorption).
Blood tests 
- Routine blood tests may reveal anaemia, high CRP or low albumin; which shows a high correlation for the presence of an organic disease. In this setting, microcytic anaemia usually implies iron deficiency and macrocytosis can be caused by impaired folic acid or B12 absorption or both. Low cholesterol or triglyceride may give a clue toward fat malabsorption. Low calcium and phosphate may give a clue toward osteomalacia from low vitamin D.
- Specific vitamins like vitamin D or micro nutrient like zinc levels can be checked. Fat soluble vitamins (A, D, E & K) are affected in fat malabsorption. Prolonged prothrombin time can be caused by vitamin K deficiency.
- Serological studies. Specific tests are carried out to determine the underlying cause.
- IgA Anti-transglutaminase antibodies or IgA Anti-endomysial antibodies for Coeliac disease (gluten sensitive enteropathy).
Stool studies 
- Microscopy is particularly useful in diarrhoea, may show protozoa like Giardia, ova, cyst and other infective agents.
- Fecal fat study to diagnose steatorrhoea is rarely performed nowadays.
- Low fecal pancreatic elastase is indicative of pancreatic insufficiency. Chymotrypsin and pancreolauryl can be assessed as well
Radiological studies 
- Barium follow through is useful in delineating small intestinal anatomy. Barium enema may be undertaken to see colonic or ileal lesions.
- CT abdomen is useful in ruling out structural abnormality, done in pancreatic protocol when visualising pancreas.
- Magnetic resonance cholangiopancreatography (MRCP) to complement or as an alternative to ERCP.
Interventional studies 
- OGD to detect duodenal pathology and obtain D2 biopsy (for coeliac disease, tropical sprue, Whipple's disease, abetalipoproteinaemia etc.)
- Enteroscopy for enteropathy and jejunal aspirate and culture for bacterial overgrowth
- Capsule Endoscopy is able to visualise the whole small intestine and is occasionally useful.
- Colonoscopy is necessary in colonic and ileal disease.
- ERCP will show pancreatic and biliary structural abnormalities.
Other investigations 
- 75SeHCAT test to diagnose bile acid malabsorption in ileal disease or primary bile acid diarrhea.
- Glucose hydrogen breath test for bacterial overgrowth
- Lactose hydrogen breath test for lactose intolerance
- Sugar probes or 51Cr-EDTA to determine intestinal permeability.
Obsolete tests no longer used clinically 
- D-xylose absorption test for mucosal disease or bacterial overgrowth. Normal in pancreatic insufficiency.
- Bile salt breath test (14C-glycocholate) to determine bile salt malabsorption.
- Schilling test to establish cause of B12 deficiency.
Treatment is directed largely towards management of underlying cause:
- Replacement of nutrients, electrolytes and fluid may be necessary. In severe deficiency, hospital admission may be required for nutritional support and detailed advice from dietitians. Use of enteral nutrition by naso-gastric or other feeding tubes may be able to provide sufficient nutritional supplementation. Tube placement may also be done by percutaneous endoscopic gastrostomy, or surgical jejunostomy. In patients whose intestinal absorptive surface is severely limited from disease or surgery, long term total parenteral nutrition may be needed.
- Pancreatic enzymes are supplemented orally in pancreatic insufficiency.
- Dietary modification is important in some conditions:
- Antibiotic therapy to treat Small Bowel Bacterial overgrowth.
- Cholestyramine or other bile acid sequestrants will help reducing diarrhoea in bile acid malabsorption.
See also 
- Jensen, Jonathan E. "Malabsorption Syndromes - Page 1". Colorado center for digestive disorders. Archived from the original on 2007-04-11. Retrieved 2007-05-10.
- Gasbarrini G, Frisono M: Critical evaluation of malabsorption tests; in G. Dobrilla, G. Bertaccini, G. Langman (Editor) (1986). Problems and Controversies in Gastroenterology. New York: Raven Pr. pp. 123–130. ISBN 88-85037-75-5.
- Bai J (1998). "Malabsorption syndromes". Digestion 59 (5): 530–46. doi:10.1159/000007529. PMID 9705537.
- Walker-Smith J, Barnard J, Bhutta Z, Heubi J, Reeves Z, Schmitz J (2002). "Chronic diarrhea and malabsorption (including short gut syndrome): Working Group Report of the First World Congress of Pediatric Gastroenterology, Hepatology, and Nutrition". J. Pediatr. Gastroenterol. Nutr. 35 Suppl 2: S98–105. doi:10.1097/00005176-200208002-00006. PMID 12192177.
- M. S Losowsky, (1974). Malabsorption in clinical practice. Edinburgh: Churchill Livingstone. ISBN 0-443-01007-2.
- health a to z"Malabsorption syndrome". Retrieved 2007-05-10.
- Bertomeu A, Ros E, Barragán V, Sachje L, Navarro S (1991). "Chronic diarrhea with normal stool and colonic examinations: organic or functional?". J. Clin. Gastroenterol. 13 (5): 531–6. doi:10.1097/00004836-199110000-00011. PMID 1744388.
- Read N, Krejs G, Read M, Santa Ana C, Morawski S, Fordtran J (1980). "Chronic diarrhea of unknown origin". Gastroenterology 78 (2): 264–71. PMID 7350049.
- Thomas P, Forbes A, Green J, Howdle P, Long R, Playford R, Sheridan M, Stevens R, Valori R, Walters J, Addison G, Hill P, Brydon G (2003). "Guidelines for the investigation of chronic diarrhoea, 2nd edition". Gut. 52 Suppl 5 (90005): v1–15. doi:10.1136/gut.52.suppl_5.v1. PMC 1867765. PMID 12801941..
- Practice guideline from World Gastroenterology Organisation
- Tests for malabsorption; from British Society for Gastroenterology