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Digestive malabsorption is characterized by increased elimination of nutrients due to insufficient assimilation through the intestinal mucosa. Chronic diarrhea with greasy stools, combined with the presence of biological deficiencies, should raise the suspicion of malabsorption. The first-line test to confirm the diagnosis of malabsorption is a 24-hour fecalogram with a search for steatorrhea. If the diagnosis is confirmed, an etiological work-up should be carried out, combining oesogastroduodenal endoscopy with duodenal and bulbar biopsies (celiac disease, Biermer’s disease, lambliasis, Whipple’s disease), testing for antibodies specific to celiac disease and Biermer’s disease (anti-transglutaminase, anti-intrinsic factor, and anti-parietal cell antibodies), fecal elastase (exocrine pancreatic insufficiency), immunoglobulin weight assay, and plasma protein electrophoresis (primary immunodeficiency). Alpha-1-antitrypsin clearance should be performed in cases of associated edematous syndrome (exudative enteropathy). Once an organic etiology has been ruled out, respiratory tests may be performed, in particular a glucose breath test to check for small intestinal bacterial overgrowth (SIBO). In the absence of diagnostic tests available in France, cholestyramine may also be tried as a trial treatment in the event of bile acid malabsorption.