Which kidney stone type is most closely associated with infection by urease-producing bacteria and alkaline urine?

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

Answer: (D)

Infections with urease-producing bacteria raise urine pH, and that alkaline environment drives the formation of struvite stones. Urease splits urea into ammonia, which increases the urine pH. When urine is alkaline, magnesium, ammonium, and phosphate readily precipitate as magnesium ammonium phosphate, the composition of struvite stones. These infection-related stones often grow large and spread into a characteristic staghorn shape within the kidney, and Proteus species are classic culprits. Other stone types form for different reasons: calcium oxalate stones come from high calcium or oxalate levels and aren’t driven by infection or pH; uric acid stones form in acidic urine and relate to purine metabolism; cystine stones arise from a genetic transport defect and tend to appear earlier in life. Thus, the association with urease-producing bacteria and alkaline urine points to struvite stones.