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HelpTest ID EFPO Electrolyte and Osmolality Panel, Feces
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 |
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
Reporting Name
Electrolyte and Osmolality Panel, FSpecimen Type
FecalCollection Container/Tube: Stool container (Supply 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 |
|---|---|---|
| Fecal | Frozen (preferred) | 14 days |
| Refrigerated | 7 days | |
| Ambient | 48 hours |
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)
Reference Values
No established reference values
Day(s) Performed
Monday through Friday; evening
Report Available
Same day/1 dayPerforming Laboratory
Mayo Medical Laboratories in Rochester
CPT Code Information
82438-Chloride
83735-Magnesium
84302-Sodium
84100-Phosphorus
84999 x 2-Osmolality, Potassium