Nephrology · Internal Medicine

Fractional Excretion of Potassium (FEK) calculator

Enter the published formula inputs below to calculate and interpret this score.

Clinical inputs

Urine potassium (mmol/L)

Serum potassium (mmol/L)

Urine creatinine (mg/dL)

Serum creatinine (mg/dL)

Result

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Formula inputs

Urine potassium (mmol/L)Accepted range: 1 to 200
Serum potassium (mmol/L)Accepted range: 1 to 10
Urine creatinine (mg/dL)Accepted range: 1 to 500
Serum creatinine (mg/dL)Accepted range: 0.1 to 20

Primary source

Ethier JH et al. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis. DOI: 10.1016/S0272-6386(12)80048-7. PMID: 2321644. Scope: fractional excretion of potassium (%) = (urine K × serum creatinine) / (serum K × urine creatinine) × 100 using paired urine and serum samples. (1990)

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