Electrolytes and Osmolality Panel, Stool

Electrolyte and Osmolality Profile, Fecal

Test Codes

EPIC: LAB1231976, Beaker: Electrolytes, Quest: 31595

Department

Send Outs

Instructions

NOTE: Includes:

• Sodium, Feces
• Potassium, Feces
• Chloride, Feces

Specimen Collection Criteria

Collect:  24-hour, 48-hour, 72-hour or random liquid stool.

Only watery liquid feces are an acceptable specimen. In the event a formed fecal specimen is submitted, the test will not be performed and will be cancelled.

• 24-hour, 48-hour or 72-hour Collection:  Keep feces refrigerated during collection.
• Random: 10.0 mL random watery liquid fecal collected in a plastic screw-cap container.

Physician Office/Draw Specimen Preparation

Refrigerate (2-8°C or 36-46°F) the specimen immediately after collection. Freeze (-20°C/-4°F or below) specimens that will not be received in the Laboratory within two hours of collection.

Preparation for Courier Transport

Transport: Stool specimen refrigerated (2-8°C or 36-46°F) or frozen (-20°C/-4°F or below).

Rejection Criteria

• Formed (solid) stool specimens.
• Specimens not collected and processed as indicated.

In-Lab Processing

The specimen should be frozen (-20°C/-4°F or below) if not analyzed within two hours of collection.

24-hour, 48-hour or 72-hour Collection:  Transport the entire collection in the original collection kit. (Minimum: 5.0 g) Do not add saline or water to liquefy specimen. Indicate time and volume.

Random Collection: Transfer 10.0 mL stool to unpreserved stool transport vial. (Minimum: 2.0 mL) Do not add saline or water to liquefy specimen. Indicate time and volume.

CRITICAL FROZEN. Separate specimens must be submitted when multiple tests are ordered.

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 1 month

Laboratory

Sent to Quest Diagnostics Nichols Institute, Chantilly VA.

Performed

Information not provided.

Reference Range

By report.

Test Methodology

Coulometric Titration, Flame Photometric.

Clinical Utility

Electrolytes, Feces – This panel measures sodium, potassium, and chloride in liquid stool. Measurements of electrolytes and osmotic gap in liquid stool help differentiate between secretory and osmotic diarrhea and, thus, guide further evaluation of chronic diarrhea [1,2].

Diarrhea can be categorized as secretory or osmotic depending on how the water content of stool is drawn in the intestine lumen. Secretory diarrhea is caused by defective electrolyte absorption that increases the stool's electrolyte levels. Conditions associated with secretory diarrhea include infection, neuroendocrine tumors, congenital chloridorrhea, intestinal resection, and diffuse mucosal disease [1]. Osmotic diarrhea is caused by the osmotic effect of a substance that retains water in the intestine lumen and leads to decreased electrolyte levels in the stool. Conditions associated with osmotic diarrhea include ingesting poorly absorbed solutes (e.g., sorbitol, mannitol, and laxatives containing magnesium) and enzyme dysfunction (e.g., lactose intolerance) [2].

Osmotic gap, calculated as the difference between the stool osmolality and twice the sum of the stool sodium and potassium levels, is useful in assessing the contribution of stool electrolytes to osmolality and differentiating between secretory and osmotic diarrhea [1,2].A theoretical fecal osmolality, approximately the same as plasma osmolality (290 mOsm/kg), is used in the calculation.

Measurement of chloride in liquid stool aids in the diagnosis of congenital or secondary chloridorrhea, which is characterized by increased excretion of chloride in stool. Low levels of chloride in liquid stool may also be seen in sodium sulfate-induced diarrhea [2].

The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.

Reference

1. Schiller LR. Pract Res Clin Gastroenterol. 2012;26(5):551-562.
2. Block DR, et al. Body fluids. In: Rifai R, et al. eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier Inc; 2022.

CPT Codes

82438, 84302, 84311.

Contacts

Last Updated

11/19/2025