Health Questions and Answers

Question: Which three diagnostic features can distinguish secretory from osmotic diarrhea?


  1. The stool osmolar gap is < 50 mOsm/kg in secretory diarrhea but is > 50 mOsm/kg in osmotic diarrhea.
  2. Secretory diarrhea is typically unrelated to ingested foods or solutes and persists during a 24-72-hour fast, whereas osmotic diarreha stops when ingestion of the offending solute ends.
  3. Patients with a pure secretory diarrhea do not have WBCs, RBCs, or fat in their stool.

Reference: Sleisenger MH, Fordtran JS (eds): Gastrointestinal Disease: Pathophysiology, Diagnosis, and Management, 7th ed. Philadelphia, W.B. Saunders, 2003

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