Renal Stones: Risk Factors

Key points

• Renal stone risk factors include low urine volume, hypercalciuria, hyperoxaluria, hypocitraturia, hyperuricosuria, high dietary sodium and relevant metabolic/inherited disorders.
• High dietary oxalate can contribute to calcium oxalate stones, particularly with low dietary calcium or enteric hyperoxaluria.
• Renal tubular acidosis , particularly distal (type 1) RTA, predisposes to calcium phosphate stones through alkaline urine and hypocitraturia.
• Medullary sponge kidney and ADPKD can be associated with nephrocalcinosis/nephrolithiasis.
• Beryllium or cadmium exposure is not a core MRCP renal-stone risk factor and should not be memorised as a standard association.
• Urate-stone risk factors: persistently low urine pH is the major determinant; hyperuricosuria, obesity/metabolic syndrome, high purine intake and gout may contribute. Hyperuricaemia is not required.
• Stone trap: distal RTA → alkaline urine + hypocitraturia → calcium phosphate stones.
• Urate stone clue: persistently acidic urine is the key determinant; uric acid stones are radiolucent on plain X-ray.