Stool Osmotic Gap Calculator
Estimate stool osmotic gap from stool sodium and potassium.
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Estimated stool osmotic gap
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Estimate using assumed stool osmolality; no mechanism is assigned
Electrolyte contribution
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Assumed stool osmolality: 290 mOsm/kg
About
The stool osmotic gap is an estimated difference between an assumed stool osmolality of 290 mOsm/kg and the osmotic contribution of measured stool sodium and potassium. It is a physiologic reference calculation, not a direct measurement of sample osmolality or a stand-alone classification of diarrhea.
Formula
Interpretation
What the result represents: An estimate of stool osmoles not represented by sodium and potassium salts.
Input units: Stool sodium and potassium are entered in mEq/L; for these monovalent ions the numeric values equal mmol/L.
Worked example: Sodium 30 and potassium 20 gives 290 − 2 × (30 + 20) = 190 mOsm/kg.
Applicable population: Selected evaluations of watery diarrhea when properly collected stool electrolytes are available.
Interpretation limitations: Collection dilution, storage, contamination, fermentation, and processing can alter results. Interpretation also depends on history, fasting response, medicines or laxatives, and other stool studies. No diarrhea mechanism or treatment is assigned here.
FAQ
Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.