Fractional Excretion of Potassium (FEK) Calculator

Calculate the fractional excretion of potassium to evaluate renal potassium handling.

Aug 31, 2026 Renal #fractional-excretion #fek #potassium

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All fields required unless noted

Urine potassium (mEq/L)

Serum potassium (mEq/L)

Serum creatinine (mg/dL)

Urine creatinine (mg/dL)

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Enter your values and press Calculate to see the result.

Formula & Clinical Notes

Formula

FEK = (UK × SCr) / (SK × UCr) × 100

Clinical Notes

FEK reflects renal potassium excretion and is used to distinguish renal (high FEK) from extrarenal (low FEK) causes of hypokalemia. It can also help evaluate hyperkalemia of renal origin. Values should be interpreted with the serum potassium and acid-base status.

Sources

StatPearls — Renal Function Tests