Fractional Excretion of Urea (FEUrea)
Determines the cause of renal failure. Similar to the FENa, but can be used on patients on diuretics.
Management
In patients with acute kidney and suspected obstructive uropathy, consider bedside ultrasound to evaluate for hydronephrosis, bladder distention, etc. Empiric Foley catheter placement may also be valid in some settings, though it may also be associated with complications, and does not rule out ureteral obstructions above the bladder.