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Allopurinol Hyperuricosuria Calcium Stones — ESENeph MCQ

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ModerateRenal Stone DiseaseAllopurinol Hyperuricosuria Calcium StonesESENeph

A 45-year-old man with CKD G3a and recurrent calcium oxalate stones undergoes metabolic evaluation. His 24-hour urine shows elevated uric acid (5.2 mmol/day). Serum urate is normal (380 umol/L). His urinary calcium and oxalate are normal. What treatment is appropriate for reducing calcium oxalate stone recurrence in this setting?

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Correct answer: B — Allopurinol – reduces urinary uric acid excretion, removing uric acid crystals that serve as nidi for calcium oxalate heterogeneous nucleation

Isolated hyperuricosuria is a recognised cause of calcium oxalate stone formation through epitaxial (heterogeneous) nucleation – uric acid crystals in the urine provide a surface for calcium oxalate crystallisation. The Ettinger 1986 RCT demonstrated that Allopurinol significantly reduced calcium oxalate stone recurrence in patients with isolated hyperuricosuria and normocalciuria. Allopurinol 100-300 mg daily reduces urinary uric acid to below the saturation threshold. This is different from treating uric acid stones (where urinary alkalinisation is primary).

Reference: EAU 2024 – Urolithiasis; Ettinger et al 1986 – Allopurinol RCT