Fractional Excretion of Potassium

Aka: Fractional Excretion of Potassium, FEK

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II. Indications

  1. Hyperkalemia

III. Precautions

  1. Results altered by Hyperkalemia Management
  2. Obtain lab sample prior to intervention if possible
    1. Do not delay treatment in emergent Hyperkalemia

IV. Labs

  1. Serum Potassium and Serum Creatinine
  2. Spot urine for Urine Potassium and Urine Creatinine

V. 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)

VI. 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

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