Sodium, Feces

Test Code

NAFE

Quest Code

8833

CPT Codes
84302

Preferred Specimen

10 mL random watery liquid fecal collected in a plastic screw-cap container, or 24-hour, 48-hour or 72-hour watery liquid fecal collected in a plastic screw-cap container

Minimum Volume

2 mL

Instructions

Submit a frozen specimen of watery liquid feces in a plastic screw-cap container. Keep feces refrigerated during collection and transport frozen. 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.

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.

Transport Temperature

Frozen

Specimen Stability

Room temperature: Unacceptable
Refrigerated: 7 days
Frozen: 60 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Specimens in paint cans • Formed stool • Specimens received refrigerated

Methodology
Flame Photometric

FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by FDA. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.

Setup Schedule

P.M. Sets up 5 days a week.

Report Available

Maximum Laboratory Turn Around Time 4 days.

Reference Range

See Laboratory Report

Clinical Significance

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.

Performing Laboratory
Quest Diagnostics Chantilly Nichols Institute
14225 Newbrook Dr.
Chantilly, VA 20151-2228

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.