Management of Uric Acid and Calcium Oxalate Stones

Uric Acid Stones

• The American Urological Association recommends potassium citrate as the first-line therapy for uric acid stones, targeting a urinary pH of 6.0-6.5 to dissolve existing stones and prevent recurrence, with a strength of evidence of high 1, 2
• Urinary alkalinization with potassium citrate is the cornerstone of management because most uric acid stone formers have unduly acidic urine, with a pH <5.5, rather than hyperuricosuria as the primary problem 1, 2
• Allopurinol should NOT be used as first-line therapy for uric acid stones unless hyperuricosuria is documented, as reducing uric acid excretion will not prevent stones in patients with acidic urine, with a strength of evidence of moderate 1, 2
• Potassium citrate is preferred over sodium citrate because sodium loading may increase urinary calcium excretion and promote mixed stone formation, with a strength of evidence of low 1, 2
• Critical pitfall: Avoid raising urinary pH above 7.0, as this increases the risk of calcium phosphate stone formation, with a strength of evidence of high 2
• Obtain 24-hour urine testing within 6 months of initiating treatment to assess metabolic response, then annually, with a strength of evidence of moderate 1
• Fluid intake should be sufficient to produce at least 2 liters of urine output daily, with a strength of evidence of high 2
• Sodium restriction, targeting ≤2,300 mg/day, helps prevent mixed stones by reducing urinary calcium excretion, with a strength of evidence of moderate 2
• Maintain normal dietary calcium intake, 1,000-1,200 mg/day, to bind oxalate in the gut and prevent calcium oxalate component formation, with a strength of evidence of high 2

Calcium Oxalate Stones

• For calcium oxalate stones, management focuses on increasing fluid intake, normalizing dietary calcium, 1,000-1,200 mg/day, restricting sodium, and using potassium citrate for hypocitraturia, with a strength of evidence of high 3, 1
• Counsel patients to consume 1,000-1,200 mg/day of dietary calcium from food sources, as higher dietary calcium intake independently reduces stone risk by binding intestinal oxalate, with a strength of evidence of high 3
• Limit sodium intake to ≤2,300 mg/day, as dietary sodium increases urinary calcium excretion, with a strength of evidence of moderate 3
• Important caveat: Calcium supplements may increase stone risk, unlike dietary calcium, with a strength of evidence of moderate 3
• Offer potassium citrate to patients with hypocitraturia, as prospective RCTs demonstrate reduced stone recurrence, with a strength of evidence of high 1
• Thiazide diuretics should be offered to patients with high or relatively high urinary calcium and recurrent stones, with a strength of evidence of moderate 3
• Increase fluid intake to achieve at least 2 liters of urine output daily, with a strength of evidence of high 3
• Obtain 24-hour urine collection to measure volume, pH, calcium, oxalate, citrate, uric acid, and sodium to guide targeted therapy, with a strength of evidence of moderate 3, 1
• Follow-up metabolic testing should occur within 6 months of treatment initiation, then annually or more frequently based on stone activity, with a strength of evidence of moderate 1
• For mixed uric acid and calcium oxalate stones, potassium citrate addresses both components by raising pH and increasing citrate, with a strength of evidence of low 2