Last updated October 5, 2026 · Report an error
Fractional Excretion of Urea (FEUrea), the standard published alternative to FENa for patients on diuretics (where FENa can be less reliable, since diuretics affect sodium handling directly): FEUrea % = (Urine urea x Serum creatinine) / (Serum urea x Urine creatinine) x 100. Pure arithmetic on four lab values. Commonly cited bands: under 35% suggestive of a prerenal cause, over 50% suggestive of an intrinsic renal cause — reference only. For general reference and educational purposes only — not a medical diagnosis. Consult a doctor for actual kidney function assessment.
How it works
Enter urine urea, serum urea (BUN), urine creatinine, and serum creatinine. The tool applies the standard FEUrea formula.
- Enter urine urea (mg/dL).
- Enter serum urea / BUN (mg/dL).
- Enter urine creatinine (mg/dL).
- Enter serum creatinine (mg/dL).
- Click Calculate to see your results.
Examples
Urine urea 900, Serum urea 30, Urine Cr 60, Serum Cr 1.5
FEUrea = (900 x 1.5) / (30 x 60) x 100 = 1350 / 1800 x 100 = 75% — commonly cited as suggestive of an intrinsic renal cause.
Who should use it
- Reviewing acute kidney injury labs in a patient on diuretics.
- Nephrology education about AKI classification on diuretics.
Industry applications
- Nephrology and critical care reference
- Emergency medicine education
Advantages
- Standard, published alternative when FENa is unreliable.
- Uses routinely available lab values.
Limitations
- Less studied historically than FENa.
- A single-point calculation — not a complete clinical picture on its own.
Common mistakes to avoid
- Using FEUrea in a patient not on diuretics, where FENa is generally the preferred standard test.
- Mixing up urine and serum values for urea versus creatinine.
Best practices
- Reserve FEUrea specifically for patients on diuretics, per commonly cited nephrology guidance.
Tips
- FEUrea is typically used specifically when a patient's diuretic use makes FENa hard to interpret.