Management of Calcium Oxalate Stones with Hyperuricemia

Diagnostic Priorities

• The American Urological Association recommends obtaining 24-hour urine collection measuring volume, pH, calcium, phosphorus, magnesium, uric acid, citrate, sodium, oxalate, and creatinine to assess stone risk 1
• Measure serum calcium, phosphate, uric acid, and creatinine to evaluate metabolic abnormalities 1, 3
• Analyze stone composition if available to guide treatment 1, 4

Primary Treatment Strategy

• The American Urological Association recommends starting potassium citrate 30-100 mEq/day to alkalinize urine and increase citrate excretion 1, 2
• Target urinary pH of 6.0-6.5 to dissolve uric acid and prevent calcium phosphate precipitation 1, 2
• Do not raise pH above 7.0, as this increases calcium phosphate stone risk 2, 4
• Reserve allopurinol for patients with hyperuricosuria (>800 mg/day in men, >750 mg/day in women) 1, 4

Dietary Modifications

• Increase fluid intake to achieve at least 2.5 liters of urine output daily 1, 3, 4
• Maintain normal dietary calcium intake (1,000-1,200 mg/day) and do not restrict calcium 3, 4
• Limit sodium to ≤2,300 mg/day to reduce urinary calcium excretion 2, 4
• Reduce animal protein intake to decrease urinary calcium and uric acid excretion 3

Monitoring Protocol

• Obtain repeat 24-hour urine collection within 6 months of starting potassium citrate to verify urinary pH and citrate levels 1, 4
• Check serum potassium within 1-2 months, as potassium citrate can cause hyperkalemia 1
• Verify stone activity has decreased or ceased 1

When to Add or Modify Therapy

• Add thiazide diuretic if 24-hour urine calcium exceeds 200 mg/day 4
• Monitor for thiazide-induced hypokalemia and glucose intolerance with periodic blood testing 1, 4
• Consider adding allopurinol if hyperuricosuria is documented and stones persist despite potassium citrate 1, 4