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FEUrea Calculator
The fractional excretion of urea (FEUrea) plays the same role as the FENa in acute kidney injury, but urea handling is much less affected by loop diuretics. It is the traditional alternative when a patient has already received diuretics and a FENa would be misleading.
Enter the values or tick the options above — the result updates automatically.
How to interpret the result
| FEUrea | Traditional interpretation in acute kidney injury |
|---|---|
| Below 35% | Prerenal pattern. |
| 35–50% | Indeterminate. |
| Above 50% | Tubular injury pattern (for example acute tubular necrosis). |
FEUrea has its own limits: it is affected by osmotic diuresis, high protein intake or catabolic states, and like FENa it should never be read in isolation. Compare it with the FENa when no diuretics have been given — the two usually agree.
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Frequently asked questions
When should FEUrea be used instead of FENa?
When the patient has received diuretics, especially loop diuretics. Diuretics raise urinary sodium and make FENa look falsely "tubular", while urea handling — and therefore FEUrea — is much less affected.
What FEUrea suggests a prerenal cause?
Below 35% is the classic prerenal pattern and above 50% the tubular injury pattern, with 35–50% indeterminate.
Which urea values does the formula need?
Urine and blood urea expressed the same way. This calculator expects urea nitrogen in mg/dL (the BUN convention) for both. If a laboratory reports urea in mmol/L, the same value must be used on both sides of the equation — the units cancel, but the convention must match.