A 45-year-old woman presents with recurrent urinary tract infections. Plain radiograph shows a large branching calculus filling the left renal pelvis and extending into all major calyces. Urine culture grows Proteus mirabilis. Which organism property explains this stone composition, and what is the preferred treatment?

• A Urease production; percutaneous nephrolithotomy ✓
• B Oxalate decarboxylase; extracorporeal shock wave lithotripsy
• C Alkaline phosphatase secretion; open nephrolithotomy
• D Citrate fermentation; flexible ureteroscopy

Explanation

Urease-producing organisms such as Proteus mirabilis split urea into ammonia, alkalinising the urine and precipitating magnesium ammonium phosphate (struvite) stones, which grow rapidly into staghorn calculi. Untreated, they lead to chronic infection, xanthogranulomatous pyelonephritis and progressive renal destruction. Percutaneous nephrolithotomy is the first-line treatment because it achieves the highest stone-free rates for large branched calculi; ESWL monotherapy leaves infected fragments behind, and open surgery is now rarely required.

Reference: Campbell-Walsh-Wein Urology, 12th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.