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Fractional Excretion of Urea (FEUrea)

FEUrea = (urine urea × plasma creatinine) ÷ (plasma urea × urine creatinine) × 100. FEUrea ≤35% suggests prerenal AKI and >50% suggests ATN; unlike FENa it remains useful after diuretics.

  • BUN / serum urea (mg/dL or mmol/L)
  • Urine urea (UUN) (mg/dL or mmol/L)
  • Serum creatinine (mg/dL or µmol/L)
  • Urine creatinine (mg/dL or µmol/L or mmol/L)
—

Interpretation

ResultMeaning
≤ 35%Prerenal
35–50%Indeterminate
> 50%ATN

Formula

FEUrea (%) = (U_urea × P_Cr) ÷ (P_urea × U_Cr) × 100 (urea and creatinine each in matching units for plasma and urine).

Clinical pearls

  • Most useful when the patient has received diuretics, which invalidate FENa.
  • Less reliable in sepsis, older adults and with osmotic diuresis (glycosuria, mannitol).

Examples

feurea bun 40 urine urea 300 cr 2 urine cr 100fractional excretion of urea: serum urea 18 mmol/L, urine urea 150 mmol/L, creatinine 220 umol/L, urine creatinine 6 mmol/L

FAQ

What FEUrea suggests prerenal AKI?

35% or less; values above 50% suggest acute tubular necrosis.

Why use FEUrea instead of FENa?

Urea reabsorption is largely passive and less affected by loop or thiazide diuretics.

Evidence

  1. Carvounis CP, Nisar S, Guro-Razuman S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int 2002;62:2223–9.

Nephrology & Electrolytes · Reviewed 2026-10-14 · Methodology