Patterns of malabsorption !
- Mechanism
- For completeness
Malabsorption happens when luminal digestion, the absorbing mucosa or the lymphatic exit fails; each failure leaves its own footprint.
Updated 2026-11-01
Also called: Maldigestion, Steatorrhea
See it in 3D: Duodenum · Jejunum · Ileum · Pancreas · Liver
What it is
Absorbing a nutrient takes three steps: digesting it in the lumen (pancreatic enzymes and bile), taking it up at the mucosa (healthy enterocytes with enough surface) and moving it on into blood or lymph. Sorting malabsorption by the step that fails makes the findings easier to read: which nutrients are missing, where the lesion is and which test confirms it.
How it works, step by step
- If enzymes or bile are missing, large nutrients (especially fat) are not broken down and pass intact.
- If the mucosa flattens, surface area and disaccharidases fall: absorption of almost everything fails in the affected segment.
- Unabsorbed fat reaches the colon: bacteria hydroxylate it and the fatty acids drive water secretion (diarrhea).
- In the colon, free fatty acids bind calcium; oxalate is left free, absorbed and forms kidney stones (enteric hyperoxaluria).
- Vitamins A, D, E and K are lost with fat; B12 fails if the ileum or intrinsic factor is missing.
- Chronic nutrient loss leads to weight loss, anemia, osteomalacia and edema from hypoalbuminemia.
Where it fails and what it leaves
| Pattern | Example | Typical footprint | Pointer test |
|---|---|---|---|
| Luminal (pancreas) | Chronic pancreatitis | Large steatorrhea, normal D-xylose | Low fecal elastase |
| Luminal (bile salts) | Ileal resection or disease | Steatorrhea, B12 deficiency, oxalate stones | Surgical history; low B12 |
| Proximal mucosa | Celiac disease | Low iron, folate and calcium; low D-xylose | IgA anti-transglutaminase and duodenal biopsy |
| Lymphatic transport | Abetalipoproteinemia | No chylomicrons, acanthocytes, vitamin E deficiency | Very low plasma lipids |
Clinical notes
- Celiac disease can show up only as refractory iron deficiency anemia or early osteoporosis, without diarrhea.
- Crohn disease with ileal resection over ≈100 cm: steatorrhea from bile-salt loss; shorter resections: bile-acid diarrhea in the colon.
- Pancreatic insufficiency: steatorrhea appears when lipase falls below ≈10% of normal.
- Intestinal parasites (giardiasis) are a cause of malabsorption to consider in children in Colombia.
Test yourself
Think of the answer, then tap the question to see it.
Why does the D-xylose test help separate pancreatic from mucosal malabsorption?
D-xylose is absorbed without prior digestion; with a healthy mucosa (as in pancreatic insufficiency) its absorption is normal, and with mucosal damage (celiac disease) it is low.
Why does ileal Crohn disease favour oxalate kidney stones?
Unabsorbed fat binds calcium in the lumen; dietary oxalate is left free, absorbed in the colon and excreted in urine, where it precipitates as calcium oxalate.
Which vitamin deficiency explains a prolonged INR in a patient with steatorrhea?
Vitamin K, which is fat-soluble and absorbed with micelles; without it the liver makes poorly functional factors II, VII, IX and X.
Why does celiac disease mainly cause iron, folate and calcium deficiency?
The lesion is worst in the duodenum and proximal jejunum, where iron, calcium and folate are preferentially absorbed.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Fat digestion and absorption
- Carbohydrate digestion and absorption
- Protein digestion and absorption
- Absorption of iron, calcium and vitamin B12
- Bile and the enterohepatic circulation
- Exocrine pancreatic secretion
- Water and electrolyte absorption and how diarrhea happens
Related conditions
- Coeliac disease
- Chronic pancreatitis
- Crohn disease
- Lactose intolerance
- Abetalipoproteinemia (Bassen–Kornzweig syndrome)
- Kidney stones (urolithiasis)
- Iron deficiency anaemia
- Pernicious anaemia
In Biochemistry
- Lipase as a lab test
- Vitamin K (phylloquinone)
- Vitamin D (calcitriol)
- Cobalamin (vitamin B12)
- Folate (vitamin B9)
- Iron metabolism
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 23.7 Chemical Digestion and Absorption: A Closer Look (OpenStax (Rice University), 2022); Celiac Disease (StatPearls (NCBI Bookshelf), 2024); Chronic Pancreatitis (StatPearls (NCBI Bookshelf), 2024); Crohn Disease (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 67). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.