Use

Useful in evaluating chronic diarrhea and identifying phosphate‑containing laxative use as a contributor to osmotic diarrhea. The concentration of electrolytes in fecal water depends on dietary intake, passive transport, and exogenous substances. Measurement of fecal phosphate helps distinguish osmotic from secretory diarrhea when elevated beyond 102 mg/dL suggests phosphate‑induced diarrhea. Osmotic diarrhea often results from poorly absorbed ions or sugars, while secretory diarrhea may stem from epithelial electrolyte transport disruption or infection. Phospholipids in liposomal drug formulations or rare gammopathies (e.g., IgM) may interfere with test accuracy.