is a state arising from abnormality in digestion
of food nutrients
across the gastrointestinal(GI) tract
Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and variety of anaemias.
Some prefer to classify malabsorption clinically into three basic categories:
- (1) selective, as seen in lactose malabsorption;
- (2) partial, as observed in a-Beta-lipoproteinemia, and
- (3) total as in celiac disease.
The main purpose of the gastrointestinal tract is to digest and absorb nutrients (fat, carbohydrate, and protein), 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.
Intestinal malabsorption can be due to:
It can present in variety of ways and features might give clue to 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 result in bloating, flatulence and abdominal discomfort. Cramping pain usually suggest obstructive intestinal segment e.g. in Crohn's disease, especially if 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.
- Low serum tryptophan and clinical depression, as can happen with fructose malabsorption
There is no specific test for Malabsorption. As for most medical conditions, investigation is guided by symptoms
and signs. Moreover, tests for pancreatic function are complex and varies widely between centres.
- Specific tests are carried out to determine underlying cause.
- IgA tissue trans glutamate or IgA antiendomysium assay for gluten sensitive enteropathy.
- Microscopy is particularly useful in diarrhoea, may show protozoa like giardia, ova, cyst and other infective agents.
- Fecal fat study to diagnose steatorrhoea is less frequently performed nowadays.
- Low elastase is indicative of pancreatic insufficiency. Chymotrypsin and pancreolauryl can be assessed as well
- Endoscopy is frequently undertaken, but to visualise small intestine, which can be up to 7m long, is indeed a daunting task.
- OGD to reveal duodenal lesion also for D2 biopsy (for celiac disease, tropical sprue, Whipple's disease, A-b-lipoproteinemia etc.)
- Enteroscopy for enteropathy and jejunal aspirate and culture for bacterial overgrowth
- Colonoscopy is helpful in colonic or ileal lesion.
- Radio isotope tests e.g. 75SeHCAT, 95mTc to exclude terminal ileal disease.
- Sugar probes or sub 51Cr-EDTA to determine intestinal permeability.
- Glucose hydrogen breath test for bacterial overgrowth
- D-xylose absorption test. lower level in urine after ingestion indicates bacterial overgrowth or reduced absorptive surface. normal in pancreatic insufficiency.
- Bile salt breath test to determine bile salt malabsorption.
- Schilling test to establish cause of B12 deficiency.
- Lactose H2 breath test for lactose intolerance
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 parenteral administration, often advice from dietitian is sought. People whose absorptive surface are severely limited from disease or surgery may need long term total parenteral nutrition. Pancreatic enzymes are supplemented orally in insufficiencies.
- Dietary modification is important in some conditions. Life-long avoidance of particular food or food constituent may be needed in Celiac disease or lactose intolerance.
- Bacterial overgrowth usually respond well to course of antibiotic. Use of cholestyramine to bind bile acid will help reducing diarrhea in bile acid malabsorption.
- Practice guideline from World Gastroenterology Organisation
- Tests for malabsorption; from British Society for Gastroenterology (2003)