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Low Urine Volume Stone Risk Factor — ESENeph MCQ

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EasyRenal Stone DiseaseLow Urine Volume Stone Risk FactorESENeph

A 55-year-old man with CKD G4 and recurrent calcium oxalate stones has a 24-hour urine showing normal calcium, normal oxalate, normal urate, but very low urine volume (800 mL/day). What is the single most important modifiable risk factor?

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Correct answer: A — Low urine volume – concentrated urine increases supersaturation of all stone-forming salts; increasing fluid intake to achieve urine output >2 L/day is the most impactful single intervention for all stone types

Low urine volume is the most common and most important modifiable risk factor for kidney stones. Concentrated urine increases the supersaturation of calcium oxalate, calcium phosphate, uric acid, and cystine. The EAU 2024 and NICE NG118 guidelines recommend fluid intake sufficient to produce >2 L urine/day as the single most impactful stone prevention measure. In this patient with otherwise normal metabolic parameters, increasing fluid intake alone may prevent recurrence. Water is the primary recommendation; timing should include evening intake to prevent overnight concentration.

Reference: EAU 2024 – Urolithiasis; NICE NG118 2019