Stool Osmotic Gap
Stool osmotic gap (Eherer & Fordtran 1992): 290 − 2·(stool Na + stool K); > 100 osmotic, < 50 secretory diarrhea.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Stool sodium
- 30 mEq/L
- Stool potassium
- 15 mEq/L
Result: Stool osmotic gap 200 mOsm/kg — osmotic diarrhea (gap > 100).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Interpretation
- > 100 osmotic diarrhea, < 50 secretory, 50–100 indeterminate.
What you enter
- Stool sodium
- Stool potassium
How this is calculated
- Formula
- Gap = 290 − 2·(stool Na + stool K), fixed 290 mOsm/kg.
Eherer AJ, Fordtran JS. Fecal osmotic gap and pH in experimental diarrhea of various causes. Gastroenterology. 1992;103(2):545-551. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.