Fractional Excretion of Urea
Estimates the cause of acute kidney injury when the patient uses diuretics.
When to use
Acute kidney injury in adults using diuretics, when FENa may be falsely elevated.
Pearls and pitfalls
- FEUrea uses urea instead of sodium and is less affected by diuretics.
- The 35% cutoff for a prerenal pattern was described in patients with renal dysfunction.
- Urea can vary with catabolism, gastrointestinal bleeding and diet, limiting interpretation.
- The result is supportive and does not replace volume assessment and urine sediment.
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Formula
FEUrea (%) = (urine BUN × plasma creatinine) / (plasma BUN × urine creatinine) × 100.
Evidence
Index proposed to help distinguish prerenal from intrinsic causes of renal dysfunction, including during diuretic use.
References
- Kaplan AA, Kohn OF. Fractional excretion of urea as a guide to renal dysfunction. Am J Nephrol. 1992;12(1-2):49-54. doi:10.1159/000168417
Frequently asked questions
What is Fractional Excretion of Urea?
Estimates the cause of acute kidney injury when the patient uses diuretics. Acute kidney injury in adults using diuretics, when FENa may be falsely elevated.
How is the result calculated?
FEUrea (%) = (urine BUN × plasma creatinine) / (plasma BUN × urine creatinine) × 100.
How should the result be interpreted?
Index proposed to help distinguish prerenal from intrinsic causes of renal dysfunction, including during diuretic use.
What are the sources?
Kaplan AA, Kohn OF. Fractional excretion of urea as a guide to renal dysfunction. Am J Nephrol. 1992;12(1-2):49-54.