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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Fecal Battery

Test Code(s): FBAT / HCFBAT

CPT Code(s): 84302, 83935, 84133

Methodology: Ion Selective Electrode and Osmometry

Days Performed: Mon-Fri, dayshift, as workload dictates.

Turnaround Time: Stat: Not available stat.
Routine: 4 days.

Specimen Requirements

Specimen: Loose stool

Collection Instructions: Collect random stool specimen. Freeze immediately if collected at an outreach location.

Collection Container: Preferred: Sterile screw cap container

Collection Volume: Preferred: 5 mL
Pediatrics: 5 mL

Sample Analyzed: Stool water

Volume Required: Preferred: 5 mL
Pediatrics: 5 mL

Specimen Transport: Transport specimen to UWHC Core Laboratory (B4/220). Transport frozen specimen on dry ice if coming from outreach location.

Unacceptable Criteria: Specimens not frozen immediately or specimens that are too dry are not acceptable.


Interpretive Guidelines:

Secretory diarrhea:

18 years and up:

Two times the concentration of the sodium plus potassium=290 mOsm.


2 X ([Na] + [K]) = 290 mOsm


Osmotic diarrhea:

18 years and up:

Two times the concentration of the sodium plus potassium < 290 mOsm.


2 X ([Na] + [K]) < 290 mOsm

Additional Information:

The osmolality of stool water should be approximately equal to two times the concentration of the sodium plus the potassium, which is also approximately equal to the plasma osmolality. Fecal osmolality is frequently elevated due to bacterial breakdown of malabsorbed carbohydrates. Therefore; Fine, Kregs, and Fordtran suggest comparing the sodium and potassium results to an average plasma osmolality of 290 mOsm.


This test was performed using a modification of an FDA approved method.  The performance characteristics of this test were determined by the UWHC Clinical Laboratories and meet the standards for clinical testing.


Fecal Osmolality Fecal Electrolytes  FOSM  FK FSOD

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