Malabsorption Basics - Gut's Big Gulp
- Definition: Impaired intestinal absorption of one or more dietary nutrients.
- Phases of Absorption (L-A-D):
- Luminal: Pancreatic enzymes & bile salts digest food; micelle formation for fats.
- Absorptive (Mucosal): Nutrients cross apical membrane of enterocytes; processing within cell.
- Delivery (Post-mucosal): Transport via lymphatics (fats, fat-soluble vitamins) & portal vein (others).
- Mechanisms:
- Pre-mucosal (Luminal): Defective hydrolysis/solubilization (e.g., Pancreatic insufficiency, ↓bile salts, ZES, Bacterial overgrowth).
- Mucosal: ↓Surface area, defective enzyme/transport (e.g., Celiac disease, Whipple's, Tropical sprue, Lactase deficiency).
- Post-mucosal: Obstruction of lymphatics (e.g., Lymphoma, Intestinal lymphangiectasia, TB).
⭐ Definition of steatorrhea: >7g fecal fat/24h on a 100g fat/day diet.
Symptom Spectrum - Telltale Tummy
⭐ Weight loss despite adequate or increased oral intake is a hallmark of malabsorption.
- Key GI Symptoms:
- Chronic diarrhea, often steatorrhea (bulky, pale, foul-smelling, greasy stools)
- Abdominal distension, bloating, ↑flatus, borborygmi
- Weight loss (adults), failure to thrive (children), fatigue, anorexia
- Nutrient Deficiency Clues (Systemic Impact):
- Anemia (↓Fe, ↓B12, ↓folate): pallor, glossitis, angular stomatitis
- Bleeding (↓Vit K): easy bruising, petechiae, purpura
- Bone pain/fractures (↓Vit D, ↓Ca): osteomalacia, osteoporosis
- Neurological (↓B12, ↓Thiamine): paresthesias, ataxia; Tetany (↓Ca, ↓Mg)
- Edema (↓protein)
- Skin/Mucosal (↓Vitamins, ↓Zinc): dermatitis (e.g., herpetiformis in celiac), hyperkeratosis (↓Vit A), night blindness (↓Vit A)
Diagnostic Toolkit - Gut Sleuthing
- Initial Clues:
- Blood tests: CBC (anemia), Albumin (↓), Ca (↓), Vit D (↓), PT (↑).
- Fat Malabsorption:
- Sudan III stain (stool, qualitative).
- ⭐ > The gold standard for diagnosing fat malabsorption is quantitative 72-hour fecal fat estimation (>7g/day abnormal).
- Carbohydrate Malabsorption:
- D-xylose test: Distinguishes mucosal vs. pancreatic.
- Normal: >25mg/dL (2h serum), >4g (5h urine).
- Low in mucosal disease.
- Hydrogen breath tests (lactose intolerance; glucose for SIBO).
- D-xylose test: Distinguishes mucosal vs. pancreatic.
- Protein Malabsorption: Fecal α1-antitrypsin (protein-losing enteropathy).
- SIBO: Jejunal aspirate (>10^5 CFU/mL).
Spotlight Syndromes - Rogues' Gallery
| Feature | Celiac Disease | Tropical Sprue | Whipple's Disease |
|---|---|---|---|
| Etiology | Gluten sensitivity (HLA-DQ2/DQ8) | ?Infectious; post-infectious enteropathy | Tropheryma whipplei (Gram+ actinomycete) |
| Key Clinical | Diarrhea, wt loss, anemia, dermatitis herpetiformis | Chronic diarrhea, steatorrhea, megaloblastic anemia (folate/B12↓) | Arthralgia, wt loss, diarrhea, neuro sx (📌 WAND: Wt loss, Arthralgia, Neuro sx, Diarrhea) |
| Dx Markers | Anti-tTG IgA, Anti-EMA, Anti-DGP; HLA-DQ2/DQ8 | ↓ Folate, ↓ B12; exclusion | PCR for T. whipplei |
| Biopsy | Villous atrophy, crypt hyperplasia, ↑IELs | Partial villous atrophy, ↑IELs, chronic inflammation | PAS+ macrophages in lamina propria |
| Treatment | Lifelong gluten-free diet (GFD) | Tetracycline + Folic acid (months) | Prolonged antibiotics (Ceftriaxone then TMP-SMX) |
⭐ Anti-tissue transglutaminase (Anti-tTG) IgA antibodies are the most sensitive and specific serological screening test for Celiac Disease.
High‑Yield Points - ⚡ Biggest Takeaways
- Celiac Disease: HLA-DQ2/DQ8 linked; anti-TTG IgA antibodies; villous atrophy on biopsy.
- Tropical Sprue: Endemic areas; chronic diarrhea, malabsorption; responds to tetracycline & folic acid.
- Whipple's Disease: T. whipplei; arthralgia, weight loss, diarrhea, neurological symptoms; PAS-positive macrophages.
- Pancreatic Insufficiency: Steatorrhea; low fecal elastase-1; enzyme replacement therapy.
- SIBO: Diagnosed by carbohydrate breath tests (glucose/lactulose) or jejunal aspirate culture.
- D-xylose test: Differentiates mucosal disease (impaired absorption) from pancreatic insufficiency (normal absorption).
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