Stool osmotic gap
Separates osmotic from secretory diarrhea.
Inputs
0 of 2mEq/L
mEq/L
When to use
- Chronic watery diarrhea workup.
Pearls and pitfalls
- Below 50: secretory; above 125: osmotic.
- Use 290 rather than measured stool osmolality, which rises after collection.
Why use
A quick lab-based branch point.
Gap = 290 − 2 × (stool Na + stool K)