Expansion
Luminal, mucosal or postmucosal failure
Expansion
Luminal phase (digestion fails)
- Pancreatic insufficiency: chronic pancreatitis, cystic fibrosis. Low faecal elastase
- Bile salt deficiency: cholestasis, ileal resection, bacterial overgrowth deconjugating bile salts
Mucosal phase (absorptive surface fails)
- Coeliac disease, Crohn disease, tropical sprue, Whipple disease, giardiasis, radiation enteritis, short bowel
Postmucosal phase (transport fails)
- Intestinal lymphangiectasia, constrictive pericarditis, lymphoma obstructing lymphatics
Clinical clues: steatorrhoea with pale, offensive, floating stool; weight loss; specific deficiencies (iron and folate proximally, B12 distally, fat-soluble vitamins in fat malabsorption).
Tests: coeliac serology, faecal elastase, faecal calprotectin, duodenal biopsy, hydrogen breath testing for bacterial overgrowth and lactose intolerance, and imaging of the small bowel.
A useful discriminator is the response to pancreatic enzyme replacement, which corrects luminal but not mucosal causes.