Osmotic Gap, Feces
Use
The osmotic gap in feces, calculated as the difference between stool osmolality and twice the sum of stool sodium and potassium levels, helps differentiate osmotic versus secretory diarrhea. Osmotic diarrhea arises from poorly absorbed solutes (e.g., sorbitol, mannitol, lactose intolerance), whereas a low osmotic gap suggests secretory causes; results must be interpreted within the relevant clinical context. ([jdos.nicholsinstitute.com](https://jdos.nicholsinstitute.com/dos/prismahealth/test/909148?utm_source=openai))
Special Instructions
Not provided.
Limitations
The test is only clinically valid using watery fecal specimens; formed stool submissions will result in cancellation. Accuracy depends on using appropriate fecal consistency. ([jdos.nicholsinstitute.com](https://jdos.nicholsinstitute.com/dos/prismahealth/test/909148?utm_source=openai))
Methodology
Automated Analyzer (Clinical Chemistry)
Biomarkers
Fecal Osmotic Gap
AnalytePotassium, Feces
AnalyteSodium, Feces
Analyte
Result Turnaround Time
1-3 days
Related Documents
For more information, please review the documents below
Specimen
Other
Volume
10 mL random watery liquid fecal or 24‑/48‑/72‑hour watery liquid fecal
Minimum Volume
2 mL
Container
Plastic screw‑cap container
Collection Instructions
Collect only watery liquid feces; keep refrigerated during collection; submit frozen.
Causes for Rejection
Formed fecal specimen will result in cancellation
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | Stable up to 3 freeze‑thaw cycles |
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