stool_osmolar_gap: Stool Osmolar (Osmotic) Gap

In cliot: Clinical Indices and Outcomes Tools

Stool Osmolar (Osmotic) Gap

Description

Calculates the Stool Osmolar Gap to help differentiate between secretory and osmotic diarrhea. The gap represents the difference between the measured stool osmolality and the estimated stool osmolality contributed by electrolytes (sodium and potassium).

Usage

stool_osmolar_gap(stool_na, stool_k, stool_osmolality = 290)

Arguments

stool_na	Numeric. Stool Sodium concentration in mmol/L (or mEq/L).
stool_k	Numeric. Stool Potassium concentration in mmol/L (or mEq/L).
stool_osmolality	Numeric. Measured stool osmolality in mOsm/kg. If not measured, 290 mOsm/kg (plasma osmolality) is often used as a surrogate value. Defaults to 290.

Details

The formula used is:

Gap = Stool Osmolality_{measured} - 2 \times (Stool Na + Stool K)

Interpretation:

• < 50 mOsm/kg: Suggests Secretory Diarrhea (e.g., toxins, hormones).

• > 100 mOsm/kg: Suggests Osmotic Diarrhea (e.g., malabsorption, laxatives).

• 50 - 100 mOsm/kg: Indeterminate.

Value

A list containing:

Stool_Osmotic_Gap	The calculated gap value.
Interpretation	Diagnostic classification based on the gap.

References

Eherer AJ, Fordtran JS. Fecal osmotic gap and pH in experimental diarrhea of various causes. Gastroenterology. 1992;103(2):545-551. doi:10.1016/0016-5085(92)90845-s

Examples

# Example 1: Osmotic Diarrhea (e.g., Lactose Intolerance)
# Na 30, K 30, Meas Osm 290 -> Gap = 290 - 2(60) = 170
stool_osmolar_gap(30, 30, 290)

# Example 2: Secretory Diarrhea (e.g., Cholera)
# Na 90, K 40, Meas Osm 280 -> Gap = 280 - 2(130) = 20
stool_osmolar_gap(90, 40, 280)

cliot documentation built on Dec. 1, 2025, 1:06 a.m.