Which occurs when normally soluble material such as calcium and oxalate supersaturates the urine and begins the process of crystal formation?

• A. Urinary tract infection
• B. Cystitis
• C. Kidney stones
• D. Pyelonephritis

Answer: (C)

Supersaturation of urine with stone-forming substances triggers crystallization. When calcium and oxalate reach concentrations higher than what the urine can keep in solution, they begin to form tiny crystals in the kidney or urinary tract. These crystals can grow and stick together, eventually developing into solid stones. Calcium oxalate stones are the most common type, and they arise precisely from this crystal nucleation and growth process, rather than from infection or inflammation.

Urinary infections like those causing cystitis or pyelonephritis involve bacteria and inflammation, not crystal formation, so they don’t describe how stones form. This scenario specifically points to stone development from crystallization due to urine supersaturation, i.e., kidney stones.