Overview of Malabsorption
Malabsorption syndrome refers to a number of disorders in which nutrients from food are not absorbed properly in the small intestine.
Certain disorders, infections, and surgical procedures can cause malabsorption.
Malabsorption causes diarrhea, weight loss, and bulky, extremely foul-smelling stools.
The diagnosis is based on typical symptoms along with stool tests and sometimes a biopsy of the lining of the small intestine.
The treatment depends on the cause.
Normally, foods are digested and nutrients (proteins, carbohydrates, fats, vitamins, and minerals) are absorbed into the bloodstream mainly in the small intestine. Malabsorption may occur if a disorder
Digestion of food can be affected by disorders that prevent adequate mixing of food with digestive enzymes and acid from the stomach. Inadequate mixing may occur in a person who has had part of the stomach surgically removed. In some disorders, the body produces inadequate amounts or types of digestive enzymes, which are necessary for the breakdown of food. For example, a common cause of malabsorption is insufficient production of digestive enzymes by the pancreas, which occurs with some pancreatic diseases, or by the small intestine, which occurs in lactase deficiency (see Lactose Intolerance). Decreased production of bile, too much acid in the stomach, or too many of the wrong kinds of bacteria growing in the small intestine (see Bacterial Overgrowth Syndrome) may also interfere with digestion.
Absorption of nutrients into the bloodstream can be affected by disorders that injure the lining of the small intestine. The normal lining consists of small projections called villi and even smaller projections called microvilli, which create an enormous surface area for absorption. Surgical removal of a large section of the small intestine substantially reduces the surface area for absorption (see Short Bowel Syndrome). Infections (bacterial, viral, or parasitic), drugs such as cholestyramine, tetracycline, colchicine, and alcohol, and disorders such as celiac disease and Crohn disease all may injure the intestinal lining. Disorders that affect the flow of lymphatic fluid from the bowel into the bloodstream (the path that fats must take to enter the bloodstream), such as malformation of intestinal lymph vessels (see Intestinal Lymphangiectasia), blockage of lymph vessels due to lymphoma (cancer of the lymphatic system), or impaired entry of lymph fluid into the bloodstream due to some heart disorders, also reduce absorption.
Symptoms of malabsorption are caused by the increased passage of unabsorbed nutrients through the digestive tract or by the nutritional deficiencies that result from inadequate absorption.
Chronic diarrhea is the most common symptom of malabsorption. When there is inadequate absorption of fats in the digestive tract, stool is light-colored, soft, bulky, greasy, and unusually foul-smelling (such stool is called steatorrhea). The stool may float or stick to the side of the toilet bowl and may be difficult to flush away. The inadequate absorption of certain sugars can cause explosive diarrhea, abdominal bloating, and flatulence.
Malabsorption can cause deficiencies of all nutrients or selective deficiencies of proteins, fats, sugars, vitamins, or minerals. People with malabsorption usually lose weight or have difficulty maintaining their weight despite adequate consumption of food. Women may stop menstruating. The symptoms vary depending on the specific deficiencies. For example, a protein deficiency can cause swelling and accumulation of fluid (edema) anywhere throughout the body, dry skin, and hair loss. Anemia (caused by vitamin or iron deficiency) may cause fatigue and weakness.
Symptoms of Nutrient Deficiencies
A doctor suspects malabsorption when a person has chronic diarrhea, weight loss, anemia, and other signs of nutritional deficiencies. Malabsorption is less obvious and often more difficult to recognize in older people than in children.
Laboratory tests can help confirm the diagnosis:
A stool test that directly measures the amount of fat in stool that has been collected over 3 days is the most reliable one for diagnosing malabsorption of fat, which is present in almost all malabsorption disorders. A finding of more than 7 grams of fat in the stool daily is the hallmark of malabsorption. Also available are a few other tests that measure fat in the stool but do not require the 3-day collection of stool.
Stool samples are examined with the unaided eye as well as under the microscope. Undigested food fragments may mean that food passes through the intestine too rapidly. In a person with jaundice, stool with excess fat indicates decreased production or secretion of bile. Sometimes parasites or their eggs are seen under the microscope, suggesting that malabsorption is caused by a parasitic infection.
Blood tests and other laboratory tests can be done to detect malabsorption of other specific substances, such as lactose or vitamin B12.
Once a doctor confirms a person has a malabsorption disorder, tests are done to diagnose the cause:
A biopsy may be needed to detect abnormalities in the lining of the small intestine. The tissue is removed through an endoscope (a flexible viewing tube equipped with a light source and a camera through which a small clipper can be inserted) passed through the mouth and into the small intestine.
Imaging tests, such as video capsule endoscopy, computed tomography, or barium x-rays, and other diagnostic tests (culture of digestive bacteria, certain blood tests, or breath tests) may also be done.
Pancreatic function tests are done if the doctor thinks that the cause of malabsorption may be the insufficient production of digestive enzymes by the pancreas. However, some of these tests are complex, time-consuming, and invasive. In one test, a tube is passed through the mouth and guided into the small intestine, where intestinal fluids containing pancreatic secretions can be collected and measured. In another test, the person swallows a substance that requires pancreatic enzymes for its digestion. The products of digestion are then measured in the urine. Recently, doctors have been doing simpler and easier tests that measure levels of certain pancreatic enzymes in the stool.