Struvite stones are composed of which minerals?

• A. Magnesium ammonium phosphate
• B. Calcium oxalate
• C. Uric acid
• D. Cystine

Answer: (A)

Struvite stones form in urine that has become alkaline due to infection with urease-producing bacteria. These bacteria split urea into ammonia, raising pH and promoting precipitation of magnesium, ammonium, and phosphate as magnesium ammonium phosphate crystals. Over time these crystals grow into struvite stones, which are chemically MgNH4PO4·6H2O. That direct composition—magnesium ammonium phosphate—explains why this option is correct. In contrast, calcium oxalate stones come from calcium oxalate, uric acid stones form in acidic urine, and cystine stones arise from cystinuria, so their compositions differ. Struvite stones are often associated with urinary tract infections and can form large, branching “stag horn” calculi.