Malabsorption syndrome refers to a number of disorders in which nutrients from food are not absorbed properly in the small intestine.
Normally, foods are digested and nutrients are absorbed into the bloodstream mainly in the small intestine. Malabsorption may occur if a disorder interferes with the digestion of food or interferes directly with the absorption of nutrients.
Digestion 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, as occurs with some pancreatic diseases, or by the small intestine, as occurs in lactase deficiency. Decreased production of bile, too much acid in the stomach, or too many of the wrong kinds of bacteria growing in the small intestine 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 (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 remaining layers of the intestinal wall, such as blockage of the lymph vessels by lymphoma (cancer of the lymphatic system) or poor blood supply to the small intestine, 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 (edema) anywhere throughout the body, dry skin, and hair loss. Anemia (caused by vitamin or iron deficiency) may cause fatigue and weakness.
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. The test that directly measures fat in the stool 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. Other laboratory tests can detect malabsorption of other specific substances, such as lactose or vitamin B12.
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.
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.
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.
Last full review/revision January 2013 by Atenodoro R. Ruiz, Jr., MD