Calcium oxalate stones are the most common type of kidney stone. Which risk factor is most closely associated with calcium oxalate stone formation?

• A. Alkaline urine with infection by urease-producing bacteria
• B. Dehydration and high oxalate intake
• C. Low calcium intake
• D. Urate overproduction

Answer: (B)

Calcium oxalate stones form when urine is saturated with calcium oxalate, so factors that concentrate urine or raise urinary oxalate drive stone formation. Dehydration lowers urine volume, making the urine more concentrated and increasing the chances that calcium and oxalate will crystallize. At the same time, high intake of oxalate-containing foods raises the amount of oxalate excreted in the urine, which combines with calcium to form calcium oxalate crystals. When both of these factors are present, the urine becomes supersaturated for calcium oxalate, leading to crystal formation and stone development.

Other stone types arise from different conditions: infection with urease-producing bacteria alkalinizes urine and favors struvite stones; uric acid stones form with high uric acid levels or acidic urine. Calcium intake can influence oxalate absorption, but dehydration plus high oxalate intake are the most direct, commonly encountered risks for calcium oxalate stones.