Fractional Excretion of Urea (FEUrea)
FEUrea (%) = (U_urea × P_Cr) / (P_urea × U_Cr) × 100 with creatinine in the same units.
Calculator
How it works
What this tool does
It applies the same clearance-ratio structure as FENa, substituting urea for sodium, which can be helpful when loop diuretics confound sodium excretion.
Formula
FEUrea (%) = (U_urea × P_Cr) / (P_urea × U_Cr) × 100
References
Carvounis CP, Nisar S, Guo-Rong S. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002;62(6):2223-2229.
Dosing & care
Teaching patterns (not rules)
- Lower FEUrea: classically taught as more “prerenal-leaning” in some oliguric presentations than high FEUrea.
- Higher FEUrea: classically taught as more “intrinsic-leaning” in some series—always interpret with medications, protein intake, and non-renal urea sources.
Limitations
GI bleed, steroids, high protein catabolism, and lab variability alter urea independent of tubular physiology; FEUrea is adjunctive to—not a replacement for—clinical judgment.
AKI context (teaching)
- Compare FEUrea with FENa, urine output response to fluids, and hemodynamics rather than using either index in isolation.
- Diuretic use affects sodium handling more than urea in many cases—document why you ordered the panel.
- Nephrology referral and renal replacement thresholds follow local protocols and trends, not a single ratio.
Educational tool only—not for diagnosis or treatment decisions.