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Test Name:
Electrolyte and Osmolality Profile, Feces


  • SBMF No:
    44526
  • Performance Lab Name:
    ARUP Laboratories
  • Test Mnemonic:
    FEC PRO
  • ABN:
    Required – No ICD-9-CM code will be reimbursed
  • CPT Code:
    83735; 84302; 84999x2
  • LOINC Code:
    2693-0; 19146-0; 19146-0; 30078-0; 13363-7; 29912-3; 29911-5; 15202-5; 15207-4
  • Ref Lab Test No:
    0020699
  • Test Includes:
    Sodium
    Potassium
    Magnesium
    Osmolality
  • Also Known As:
    Osmolality and Electrolytes Profile, Feces
  • Spec Type:
    Feces, liquid, random
  • Spec Container:
    Clean (Unpreserved) Stool Transport Vial
  • Alt Spec Type:
    24-hour feces collection
  • Alt Spec Container:
    Plastic container with tightly fitting lid
  • Pref Vol:
    10.0 g
  • Min Vol:
    5.0 g
  • Spec Collect:
    Routine random or 24-hour feces collection
  • Spec Process:
    Transfer sample aliquot from well-mixed 24-hour or random feces collection to clean (unpreserved) Stool Transport Vial and freeze
    Send aliquot with notation of total time and volume on aliquot label and on requisition
  • Spec Store Transport:
    Frozen
  • Spec Stability:
    Room temperature (20-30°C): Unacceptable
    Refrigerated (2-8°C): Unacceptable
    1 month frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles
  • Spec Reject:
    Formed (non-liquid) or viscous feces sample
  • Spec Remarks:
    CRITICAL FROZEN
    Sample must be liquid
    Do not add saline or water to liquefy sample
    Test is not indicated for patients passing non-liquid feces
  • Methodology:
    Ion-Selective Electrode
    Freezing Point Depression
  • Reference Range:

    Sodium, Fecal
    Not Established

    Potassium, Fecal
    Not Established

    Magnesium, Fecal
    0-110 mg/dL

    Calculated Osmolality, Fecal
    By report

    Osmolality, Fecal (measured)
    0-16 years: 271-296 mOsm/kg
    17 years and older: 280-303 mOsm/kg

    Osmolal Gap
    By report

    Interpretive Data:
    Normal fecal fluid has an osmolality close to that of plasma (i.e., 290 mOsm/kg), a sodium concentration of about 30 mmol/L, a potassium concentration of about 75 mmol/L, and a magnesium concentration between 12 to 240 mg/dL (depending on diet) although it is usually less than 110 mg/dL. A fecal sodium greater than 90 mmol/L and an osmolal gap less than 50 mOsm/kg suggests secretory diarrhea or osmotic diarrhea due to sodium-containing laxatives. A fecal sodium less than 60 mmol/L and an osmolal gap greater than 100 mOsm/kg suggests osmotic diarrhea. Fecal sodium greater than 150 mmol/L and osmolality greater than 400 mOsm/kg suggests contamination with concentrated urine. Fecal osmolality less than 250 mOsm/kg suggests contamination with hypoosmotic urine or water.

  • Day Run:
    Sun-Sat (daily)
  • Time Reported:
    2-4 days
  • Test Type:
    CHEMISTRY

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