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Test Code ELOSF / EFPO-M Electrolyte and Osmolality Panel, Feces

Reporting Name

Electrolyte and Osmolality Panel, F

Useful For

Workup of cases of chronic diarrhea

 

Diagnosis of factitious diarrhea (where patient adds water to stool to simulate diarrhea)

Profile Information

Test ID Reporting Name Available Separately Always Performed
NA_F Sodium, F No Yes
K_F Potassium, F No Yes
CL_F Chloride, F No Yes
OSMOF Osmolality, F No Yes
MG_F Magnesium, F No Yes
OG_F Osmotic Gap, F No Yes
POU_F Phosphorus, F No Yes

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Fecal


Specimen Required


Collection Container/Tube: Stool container (T291)

Specimen Volume: 10 g

Collection Instructions: Collect a very liquid stool specimen.

Additional Information:

1. Do not send formed stool. In the event a formed stool is submitted, the test will not be performed. The report will indicate "A formed stool specimen was submitted for analysis. This test was not performed because it only has clinical value if performed on a watery stool specimen."

2. Osmolality results will be reported as mOsm/kg regardless of collection duration.

3. Sodium, chloride, and potassium will be reported as mmol/L

4. Magnesium and phosphorus will be reported as mg/dL


Specimen Minimum Volume

5 g

Specimen Stability Information

Specimen Type Temperature Time Special Container
Fecal Frozen (preferred) 14 days
  Refrigerated  7 days
  Ambient  48 hours

Reference Values

No established reference values

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; Evening

CPT Code Information

82438-Chloride

83735-Magnesium

84302-Sodium

84100-Phosphorus

84999 x 2-Osmolality, Potassium

LOINC Code Information

Test ID Test Order Name Order LOINC Value
EFPO Electrolyte and Osmolality Panel, F 88697-8

 

Result ID Test Result Name Result LOINC Value
NA_F Sodium, F 15207-4
K_F Potassium, F 15202-5
CL_F Chloride, F 15158-9
MG_F Magnesium, F 29911-5
OG_F Osmotic Gap, F 73571-2
POU_F Phosphorus, F 88713-3
OSMOF Osmolality, F 2693-0

Clinical Information

The concentration of electrolytes in fecal water and their rate of excretion are dependent upon 3 factors:

-Normal daily dietary intake of electrolytes

-Passive transport from serum and other vascular spaces to equilibrate fecal osmotic pressure with vascular osmotic pressure

-Electrolyte transport into fecal water due to exogenous substances and rare toxins (eg, cholera toxin)

 

Fecal osmolality is normally in equilibrium with vascular osmolality, and sodium is the major affector of this equilibrium. Fecal osmolality is normally 2 x (sodium + potassium) unless there are exogenous factors inducing a change in composition, such as the presence of other osmotic agents (magnesium sulfate, saccharides) or drugs inducing secretions, such as phenolphthalein or bisacodyl.

 

Osmotic diarrhea is caused by ingestion of poorly absorbed ions or sugars and can be characterized by the following:

-Stool volume typically decreased by fasting

-Fecal fluid usually has an elevated osmotic gap

-Osmotic agents such as magnesium, sorbitol, or polyethylene glycol may be the cause through the intentional or inadvertent use of laxatives

-Carbohydrate malabsorption due most commonly to lactose intolerance

-Carbohydrate malabsorption can be differentiated from other osmotic causes by a low stool pH (<6)

 

Secretory diarrhea is caused by disruption of epithelial electrolyte transport and can be characterized by the following:

-Stool volume is usually unaffected by fasting

-Fecal fluid usually has elevated electrolytes (primarily sodium and chloride) and a low osmotic gap (<50 mOsm/kg)

-Common causes include bile acid malabsorption, inflammatory bowel disease, endocrine tumors, and neoplasia

-Secretory agents such as anthraquinones, phenolphthalein, bisacodyl, or cholera toxin should also be considered

-Infection is a common secretory process; however, it does not typically cause chronic diarrhea (defined as symptoms >4 weeks)

Analytic Time

Same day/1 day

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Method Name

OG_F: Calculation

NA_F, K_F, CL_F: Indirect Ion-Selective Electrode (ISE) Potentiometry

OSMOF: Freezing Point Depression

POU_F: Photometric, Ammonium Molybdate

MG_F: Colorimetric Titration

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.