FE Urea is not altered by diuretics (in general).
Is used to differentiate between renal and prerenal ARF.
FEUrea > 40-70% (> 0.4 - 0.7 fraction) indicates renal causes.
FEUrea < 20-30% (< 0.2 - 0.3 fraction) indicates prerenal causes.
See also , and for more about ARF (acute renal failure) differential diagnosis.