Lab

Fractional Excretion of Potassium

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Fractional Excretion of Potassium, FEK

  • See Also
  1. Potassium Homeostasis
  2. Serum Potassium
  3. Urine Potassium
  4. Hyperkalemia
  5. Hypokalemia
  • Indications
  1. Hyperkalemia
  • Precautions
  1. Results altered by Hyperkalemia Management
  2. Obtain lab sample prior to intervention if possible
    1. Do not delay treatment in emergent Hyperkalemia
  • Labs
  1. Serum Potassium and Serum Creatinine
  2. Spot urine for Urine Potassium and Urine Creatinine
  • Formula
  1. FEK = (Potassium Excretion x 100)/(total filtered load)
    1. Potassium (K+) Excretion = (Urine K++) / (Serum K++)
    2. Total Load = (Urine Creatinine) / (Serum Creatinine)
  2. FEK = (uK x sCr x 100) / (sK x uCr)
  • Interpretation of Fractional Excretion of Potassium
  1. FEK <10%: Renal cause of Hyperkalemia
  2. FEK >10%: Extrarenal cause of Hyperkalemia
    1. May also be increased in Chronic Renal Failure