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Hyperuricosuria Calcium Stones — ESENeph MCQ

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HardRenal Stone DiseaseHyperuricosuria Calcium StonesESENeph

A 42-year-old man presents with recurrent calcium oxalate stones. His 24-hour urine shows elevated uric acid excretion (5.5 mmol/day) alongside elevated calcium and oxalate. Serum urate is 480 umol/L. What is the role of hyperuricosuria in calcium stone formation?

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Correct answer: D — Uric acid crystals promote heterogeneous nucleation of calcium oxalate crystals (epitaxial growth)

Hyperuricosuria is a recognised risk factor for calcium oxalate stone formation. Uric acid crystals in the urine can serve as nidi for heterogeneous nucleation (epitaxial growth) of calcium oxalate. Allopurinol reduces urinary uric acid excretion and has been shown in the Ettinger 1986 RCT to reduce calcium oxalate stone recurrence in patients with hyperuricosuria. This is an important but often overlooked mechanism of calcium stone formation.

Reference: EAU 2024 – Urolithiasis; Ettinger et al 1986 – Allopurinol for Calcium Stones