Fractional Excretion of Urea (FEUrea) Calculator

About this calculator

FEUrea measures what fraction of the urea filtered by the kidneys actually makes it into the urine: FEUrea % = (urine urea × plasma creatinine) ÷ (plasma urea × urine creatinine) × 100. It does the same job as the better-known FENa (fractional excretion of sodium) — distinguishing prerenal azotemia (kidneys are fine, blood flow is low) from intrinsic acute kidney injury like acute tubular necrosis — but urea handling isn't disrupted by diuretics the way sodium handling is, so FEUrea stays reliable in patients already on loop or thiazide diuretics.

Nephrologists and intensive care physicians use it at the bedside when a patient with rising creatinine has recently received diuretics, muddying FENa: a value under 35% suggests a prerenal cause (volume depletion, low cardiac output), while values above 50% point toward intrinsic renal injury.