mg/dL
mg/dL
mg/dL
mg/dL
How it's calculated
FEUrea (%) = (urine urea nitrogen × plasma creatinine) / (plasma urea nitrogen × urine creatinine) × 100.
Interpretation
| FEUrea | Interpretation |
|---|---|
| < 35% | Suggests prerenal azotaemia |
| 35-50% | Indeterminate |
| > 50% | Suggests intrinsic renal injury (e.g. ATN) |
Clinical use
- Used in the AKI workup specifically when the patient has received diuretics, since diuretic-induced natriuresis makes FENa unreliable in that setting — urea handling is comparatively less affected.
- Complements, rather than replaces, the overall clinical assessment (volume status, urinalysis, medication review, renal ultrasound where indicated).
- Like FENa, it is most useful in oliguric AKI and is less validated in chronic kidney disease or with contrast/other confounders.
Frequently asked questions
Why use FEUrea instead of FENa?
FENa can be falsely elevated by diuretics (which promote sodium excretion regardless of the underlying prerenal/intrinsic cause), making it unreliable in that setting — FEUrea is less affected by diuretics and is preferred when the patient has received them.
What does a FEUrea below 35% mean?
It suggests a prerenal cause of AKI — the kidneys are appropriately conserving urea in response to reduced perfusion, similar to how a low FENa suggests prerenal azotaemia.
Can FEUrea be used in every AKI patient?
It's most useful when diuretics have been given; in patients not on diuretics, FENa is generally still the more established and validated test.
References
- Kaplan AA, Kohn OF. Fractional excretion of urea as a guide to renal dysfunction. Am J Nephrol. 1992;12(1-2):49-54.
- Carvounis CP, et al. Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int. 2002.