Malabsorption: Clinical

With malabsorption, nutrients are no longer effectively absorbed in the small intestines. Nutrients can either be macronutrients, such as fats, proteins and carbs or micronutrients like vitamins and minerals. Malabsorption can either be global meaning that the absorption of all nutrients is affected or it can be partial meaning that only specific nutrients cannot be absorbed. Malabsorption presents differently based on which nutrients are being malabsorbed, the severity of the disease, and the underlying cause. Global malabsorption can present with chronic or recurrent diarrhea with pale, greasy, voluminous and terrible smelling stools and unintentional weight loss. In contrast, partial malabsorption causes symptoms specific to the nutrient involved.

With fat malabsorption, symptoms include steatorrhea - meaning fatty stools. To confirm that it’s really steatorrhea, a fecal fat test can be done to check for fat. If it’s negative and fat malabsorption is still suspected, then a 72 hours stool collection should be done because that’s the gold standard for diagnosing fat malabsorption. To do that, an individual has to have a diet that includes 70 to 120 grams of dietary fat per day, which is the equivalent of eating about 300 grams of cheese per day. Stool is collected for 72 hours, and if there’s more than 6 grams of fat per day, then it’s considered fat malabsorption. Typically if there’s steatorrhea, the stool fat exceeds 20 grams per day.

If fat malabsorption is present, then the fat soluble vitamins - A, D, E, and K, might also not be getting absorbed. Vitamin A deficiency causes symptoms like night blindness and thickened skin due to hyperkeratosis. Vitamin D deficiency causes symptoms like paresthesias, and fractures due to osteomalacia. Vitamin E deficiency can cause symptoms like muscle weakness. And finally, vitamin K deficiency causes symptoms like easy bruising, excessive bleeding from wounds, gastrointestinal bleeds, or hematuria.

With protein malabsorption, edema and muscle atrophy may be present and on the lab tests, there may be hypoalbuminemia and a low total protein level in the blood. With carbohydrate malabsorption, symptoms include watery diarrhea, flatulence, and bloating. To identify carbohydrate malabsorption, the D-xylose test can be done. That’s where an individual fasts overnight and then eats 25 grams of D-xylose, which is a monosaccharide that’s normally absorbed by the small intestine. The serum D-xylose is checked after an hour and if it’s below 20 milligrams per deciliter that suggests malabsorption. In addition, urine is collected over the next five hours as fasting continues, and if urine excretion of D-xylose is below 4.5 grams, that also suggests malabsorption. False-positive results can occur, especially in older individuals with a decreased glomerular filtration rate.