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GI & Liver

Stool Osmotic Gap

Distinguishes osmotic from secretory diarrhoea using stool electrolytes.

Written for clinicians. If you're a parent or patient, don't act on these numbers — talk to your child's doctor.

Inputs

FieldUnitNotes
Stool sodium mmol/L 0–200
Stool potassium mmol/L 0–200

FAQ

What is the Stool Osmotic Gap?

Distinguishes osmotic from secretory diarrhoea using stool electrolytes.

What inputs does the Stool Osmotic Gap need?

Stool sodium (mmol/L), Stool potassium (mmol/L).

Related guides

Stool Osmotic Gap: Separating Osmotic from Secretory Diarrhoea

Stool osmotic gap = 290 − 2 × (stool Na + stool K). A gap >100 mOsm/kg suggests osmotic diarrhoea; <50 suggests secretory. Formula, cut-offs, a worked example, and the key pitfalls.

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