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Fractional Excretion of PotassiumAka: FEK

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

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 6/1/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.