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

Allowed range: 1–200 mmol/L

Serum potassium

mmol/L

Allowed range: 1–10 mmol/L

Urine creatinine

mg/dL

Allowed range: 1–500 mg/dL

Serum creatinine

mg/dL

Allowed range: 0.1–20 mg/dL

Result

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Clinical 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

Elisaf M, Siamopoulos KC. Fractional excretion of potassium in normal subjects and in patients with hypokalaemia. Postgrad Med J. 1995;71:211-212. DOI: 10.1136/pgmj.71.834.211. PMID: 7784279. Scope: FEK+ (%) = (urine K × serum creatinine) / (serum K × urine creatinine) × 100. (1995)

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