Unexplained Renal Failure
(suspect obstruction if bladder or prostate enlarged, evidence of tumor, or urinalysis nondiagnostic)

Obstruction below bladder neck

Identify specific cause of obstruction (consider CT evaluation)

No further workup for obstruction

End

Insert bladder catheter

Diuresis

No diuresis; do renal ultrasound

Hydronephrosis; obstruction above bladder neck

No hydronephrosis

High clinical suspicion

Low clinical suspicion of obstruction

Identify site and relieve obstruction

Antegrade urogram

Retrograde urogram