Postrenal

Postrenal refers to disorders that affect urine flow downstream of the kidneys, causing impairment of kidney function due to obstruction. In the framework of acute kidney injury, postrenal causes are distinguished from prerenal (before the kidneys) and intrinsic or intrarenal causes. Obstruction can be bilateral or involve a solitary functioning kidney, and relief of blockage is central to recovery.

Causes of postrenal obstruction include bladder outlet obstruction such as benign prostatic hyperplasia, urethral stricture, neurogenic bladder, or urinary retention; and upper tract causes such as ureteral stones, malignancies, extrinsic compression, or congenital or acquired strictures. Catheter-related issues, mucus plugs, or stone fragments can also contribute to obstruction in hospitalized patients.

Clinical presentation varies with the site and duration of obstruction. Patients may have reduced urine output or, less commonly, anuria, flank or suprapubic pain, abdominal distension, or symptoms related to the underlying condition (for example, urinary retention from BPH). Physical examination may reveal a palpable bladder. Imaging, particularly ultrasound, often shows hydronephrosis and may identify the level of obstruction; CT urography can provide further detail. Laboratory testing typically shows a rise in serum creatinine and may reveal signs related to the underlying disorder.

Management centers on prompt relief of the obstruction. This may involve urinary catheterization, ureteral stenting, or percutaneous nephrostomy, followed by treatment of the underlying cause (stone removal, medical or surgical management of BPH, oncology-directed therapy). Prognosis depends on the duration and severity of obstruction; early relief can allow full recovery, while prolonged obstruction may cause lasting kidney damage.