Stool osmotic gap is calculated by using the formula:

Stool osmotic gap is calculated by using the formula : 2 x (stool + stool ) stool osmolality When it is >50, an osmotic gap is present, suggests diarrhea is due to a non absorbed dietary nutrient, e.g., a fatty acid and/or carbohydrate. When this difference is <25, a dietary nutrient is not responsible for the diarrhea. Ref: Harrison, E-18, P-2460.