Fractional Excretion of Urea (FEUrea) Calculator

Calculate FEUrea to distinguish prerenal from intrinsic acute kidney injury, especially on diuretics.

Aug 31, 2026 Renal #fractional-excretion #aki #feurea #diuretics

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All fields required unless noted

Urine urea nitrogen (mg/dL)

Serum urea nitrogen (BUN) (mg/dL)

Serum creatinine (mg/dL)

Urine creatinine (mg/dL)

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Formula & Clinical Notes

Formula

FEUrea = (UUrea × SCr) / (SUrea × UCr) × 100

Clinical Notes

FEUrea below 35% suggests prerenal azotemia, while values above 50% suggest intrinsic acute tubular injury. Because urea reabsorption is less affected by diuretics than sodium, FEUrea is preferred over FENa in patients on diuretics. FEUrea can exceed 100% in healthy subjects.

Sources

Carvounis CP, et al. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002.
StatPearls — Renal Function Tests