Postrenal Acute Kidney Injury: The Daily PANCE Blueprint
A 74-year-old man presents with 2 days of lower abdominal discomfort and dribbling small amounts of urine. He has benign prostatic hyperplasia and started diphenhydramine for insomnia last week. His blood pressure is 148/86 mm Hg, and he is afebrile. A tender, distended bladder is palpable to the umbilicus. Serum creatinine is 2.4 mg/dL, up from 1.0 mg/dL last month. Which of the following is the most appropriate next step in management?
A. Intravenous normal saline bolus
B. Renal biopsy
C. Intravenous furosemide
D. Bladder catheterization
E. CT of the abdomen with intravenous contrast
Answer and topic summary
The answer is D. Bladder catheterization
This is postrenal acute kidney injury from bladder outlet obstruction. BPH narrows the outlet, and a new anticholinergic medication such as diphenhydramine weakens the detrusor, which is a classic trigger for acute urinary retention. The next step is to relieve the obstruction with a urethral (Foley) catheter, which is both diagnostic and therapeutic. A bladder scan confirms retention when the exam is unclear, and a renal ultrasound looks for hydronephrosis. After decompression, watch for post-obstructive diuresis and replace fluids and electrolytes. Stop the anticholinergic, and start an alpha-blocker such as tamsulosin before a trial without the catheter. IV fluids treat prerenal AKI, furosemide does nothing for obstruction, contrast CT adds kidney risk without changing the first step, and biopsy is reserved for unexplained intrinsic disease.
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