Which finding supports post-renal obstruction due to BPH?

• A. Weak urinary stream
• B. Nocturia
• C. Elevated creatinine with hydronephrosis on ultrasound
• D. Frequent urination

Answer: (C)

Post-renal obstruction from BPH causes urine to back up beyond the bladder, eventually raising pressure in the kidneys. The most specific evidence that this obstruction is affecting kidney function is elevated creatinine together with hydronephrosis seen on ultrasound, which shows dilation of the renal pelvis and calyces from urine backing up into the kidney. This combination indicates that the obstruction is not just causing bladder symptoms but is impacting renal function. The other findings—weak stream, nocturia, or frequent urination—are common bladder outlet symptoms of BPH but don’t by themselves demonstrate kidney involvement or obstruction of the urinary tract upstream of the bladder.