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Related Experiment Videos

The fecal osmotic gap: technical aspects regarding its calculation.

A Duncan1, C Robertson, R I Russell

  • 1Gastroenterology Unit, Royal Infirmary, Glasgow, Scotland.

The Journal of Laboratory and Clinical Medicine
|April 1, 1992
PubMed
Summary

Accurate fecal osmotic gap calculation is key for diagnosing chronic diarrhea. Freezing point depression for osmolality measurement and plasma osmolality for gap calculation are recommended for reliable results.

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Area of Science:

  • Gastroenterology
  • Clinical Chemistry

Background:

  • The fecal osmotic gap aids in chronic diarrhea investigation.
  • Uncertainty exists regarding osmolality measurement methods and osmotic gap calculation.

Purpose of the Study:

  • To evaluate different methods for measuring fecal osmolality.
  • To determine the most appropriate method for calculating the fecal osmotic gap.

Main Methods:

  • Stool osmolality was measured using dew point and freezing point depression techniques.
  • Fecal osmotic gap was calculated by subtracting calculated osmolality from stool or plasma osmolality.
  • Electrolyte concentrations were measured in 41 patients with various diarrhea causes.

Main Results:

  • Dew point osmolality measurement underestimated results, deeming it inappropriate.

Related Experiment Videos

  • Freezing point depression provided reliable fecal osmolality measurements.
  • Calculating the osmotic gap using stool osmolality showed significant variability and poor diagnostic resolution.

    • Conclusions:

    • Freezing point depression is the preferred method for fecal osmolality measurement.
    • Calculating the fecal osmotic gap using plasma osmolality is more reliable than using stool osmolality for diagnosing diarrhea causes.