Sodium, Feces
Test Summary
This test measures sodium 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 (eg, sorbitol, mannitol, and laxatives containing magnesium) and enzyme dysfunction (eg, lactose intolerance) [2].
Stool sodium level is often measured in conjunction with stool potassium level to calculate osmotic gap, which is the difference between the stool osmolality and twice the sum of the stool sodium and potassium levels. Osmotic gap is useful in assessing the contribution of stool electrolytes to osmolality and differentiating between secretory and osmotic diarrhea [1,2].
The results of this test should be interpreted in the context of pertinent clinical and family history and physical examination findings.
References
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.
Aliases
- N/A
Specimen Collection
Special Instructions
Preferred Specimen
Minimum Volume
Instructions
Note: Specimen must be shipped frozen to reduce the odor during shipping and to minimize the risk of the container rupturing due to gas accumulation.
This test only has clinical utility if performed on a watery fecal specimen.
Stable up to 3 freeze-thaw cycles
Patient Preparation
Storage
Transport Temperature
Specimen Stability
- Room temperature: Unacceptable
- Refrigerated: 7 days
- Frozen: 60 days
Limitations
Other Acceptable Specimens
Unacceptable Specimens
Order Code
EPIC (Premier) Code
Includes
CPT Code
- 84302
Billing Code
- 670348
CPT Statement
Methodology
FDA Status
Physician Attestation of Informed Consent
Testing Laboratory
14225 Newbrook Drive
Chantilly VA, 20153
Department
Reference Range
Setup Schedule / Expected Turnaround Time
Specimen Collection
Special Instructions
Preferred Specimen
Minimum Volume
Instructions
Note: Specimen must be shipped frozen to reduce the odor during shipping and to minimize the risk of the container rupturing due to gas accumulation.
This test only has clinical utility if performed on a watery fecal specimen.
Stable up to 3 freeze-thaw cycles
Patient Preparation
Storage
Transport Temperature
Specimen Stability
- Room temperature: Unacceptable
- Refrigerated: 7 days
- Frozen: 60 days