Staghorn calculi are most commonly associated with which type of stones due to urease-producing infections?

• A. Struvite stones
• B. Calcium oxalate stones
• C. Uric acid stones
• D. Cystine stones

Answer: (A)

Staghorn stones arise from infection-related crystallization driven by urease-producing bacteria. Urease splits urea into ammonia and carbon dioxide, raising the urine pH (alkaline environment). This alkaline urine favors precipitation of magnesium ammonium phosphate, i.e., struvite, often along with carbonate apatite, leading to large, branching stones that can fill the renal pelvis and calyces. Because these stones form in the setting of infection, treating the underlying bacteria and removing the stone are essential to prevent recurrence. Other stone types—calcium oxalate, uric acid, and cystine—are not driven by urease activity and are not typically associated with this infection-related staghorn pattern.