How does volume depletion influence the risk of nephrolithiasis due to calcium oxalate stones?

How does volume depletion influence the risk of nephrolithiasis due to calcium oxalate stones?

• A. Increases risk
• B. Decreases risk
• C. No effect
• D. Only affects uric stones

Answer: (A)

When the body is volume depleted, urine becomes more concentrated because less water is available to dilute solutes. Calcium oxalate stones form when urine is supersaturated with calcium and oxalate, so concentrating these solutes increases their tendency to precipitate and form crystals that can grow into stones. Slower, more concentrated urine also means crystals spend more time in the urinary tract, promoting aggregation. Adequate hydration raises urine volume, diluting calcium and oxalate, reducing supersaturation, and lowering the risk of calcium oxalate stones.

When the body is volume depleted, urine becomes more concentrated because less water is available to dilute solutes. Calcium oxalate stones form when urine is supersaturated with calcium and oxalate, so concentrating these solutes increases their tendency to precipitate and form crystals that can grow into stones. Slower, more concentrated urine also means crystals spend more time in the urinary tract, promoting aggregation. Adequate hydration raises urine volume, diluting calcium and oxalate, reducing supersaturation, and lowering the risk of calcium oxalate stones.