How secretory and osmotic watery diarrhea distinguished?
- The most useful way to differentiate secretory and osmotic types of watery diarrhea is to measure fecal electrolytes and calculate the fecal osmotic gap.
- In many diarrheal conditions, sodium and potassium along with their accompanying anions are the dominant electrolytes in stool water.
- In secretory diarrhea, there is a failure to completely absorb electrolytes or actual electrolyte secretion by the intestine; sodium, potassium, and their accompanying anions are responsible for the bulk of osmotic activity in stool water and the retention of water within the gut lumen.
- In contrast, in osmotic diarrhea, ingestion of poorly absorbed, osmotically active substances is responsible for holding water within the gut lumen; electrolyte absorption is normal and thus sodium and potassium concentrations can become quite low.
- The fecal osmotic gap calculation takes advantage of these distinctions to differentiate the two conditions.
