Stool Osmotic Gap
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| Stool Na: |
| Stool K:
|
| Stool Osm:
|
|
|
Background
|
Stool osmotic gap =
Stool osmolality - 2 x (stool Na + stool K)
Normal fecal fluid values:
Osmolality: ~290 mOsm/kg
Na+: ~30 mmol/L
K+: ~75 mmol/L |
Secretory diarrhea
|
Diarrhea associated with a stool osmolal
gap less than 50 mOsm/kg.
Potential causes:
-Bile salt enteropathy
-Congenital diarrhea
-Drugs: (e.g. colchicine, SSRIs, prostaglandins, quinine,
cholinesterase inhibitors).
-Enterotoxin-producing bacterial pathogens:( e.g. clostridium,
cholera and shigella.)
-Hyperthyroidism
-Laxative abuse
-Lymphocytic or collagenous colitis
-Neuroendocrine tumors (Vipomas, gastrinomas, carcinoid
tumors).
-Rectal villous adenoma |
Osmotic diarrhea
|
Diarrhea associated with a stool osmolal gap
greater than 100 mOsm/kg.
Potential causes:
-Hexitols (poorly absorbed): sorbitol, mannitol, xylitol).
-Lactulose.
-Sugar intolerance (e.g. lactose intolerance).
-Unabsorbable water-soluble solutes used as laxatives: (PEG, Mg salts, Na
Phosphate). |
