What is the recommended management for calcium oxalate stones according to the European Association of Urology (EAU) guidelines?

Management of Calcium Oxalate Stones According to EAU 2025

All patients with calcium oxalate stones should increase fluid intake to achieve at least 2.5 liters of urine daily, limit sodium to 100 mEq (2,300 mg) per day, consume 1,000-1,200 mg of dietary calcium with meals, and restrict oxalate-rich foods if urinary oxalate is elevated. 1

Initial Evaluation and Risk Assessment

Metabolic testing is essential for all recurrent stone formers and should include one or two 24-hour urine collections analyzing volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine. 1

• Stone analysis by polarization microscopy should be obtained whenever possible to confirm calcium oxalate composition 2
• Serum testing should include calcium, phosphate, uric acid, and creatinine to exclude systemic causes 1, 2
• Two 24-hour urine collections are preferred over one to improve accuracy of metabolic assessment 1

Dietary Management (First-Line for All Patients)

Fluid Intake

The cornerstone of prevention is achieving urine volume of at least 2.5 liters daily through adequate fluid intake. 1, 3

• This represents a continuous protective effect, with higher volumes conferring greater benefit 1
• Beverages such as coffee, tea, wine, and orange juice may provide additional protective effects beyond hydration alone 1
• Sugar-sweetened beverages should be avoided as they increase stone risk 1

Calcium Intake

Patients should consume 1,000-1,200 mg of dietary calcium daily, preferably from food sources rather than supplements. 1

• A landmark RCT demonstrated that normal calcium intake (1,200 mg/day) reduced stone recurrence by 51% compared to low calcium intake (400 mg/day) 1
• Calcium should be consumed primarily with meals to enhance gastrointestinal binding of oxalate 1
• Calcium supplements should be avoided as they increase stone risk by 20% compared to dietary sources 1

Sodium Restriction

Sodium intake should be limited to 100 mEq (2,300 mg) daily as dietary sodium directly increases urinary calcium excretion. 1

• This restriction is particularly important when thiazide therapy is prescribed to maximize the hypocalciuric effect 1

Oxalate Restriction

Patients with relatively high urinary oxalate should limit intake of oxalate-rich foods while maintaining normal calcium consumption. 1

• The Harvard School of Public Health provides a comprehensive list of oxalate content in foods 1
• Special consideration for enteric hyperoxaluria: Patients with malabsorptive conditions (inflammatory bowel disease, Roux-en-Y gastric bypass) may require more restrictive oxalate diets and higher calcium intakes, potentially including supplements timed with meals 1

Pharmacological Management

Thiazide Diuretics (For Hypercalciuria)

Thiazide diuretics should be offered to patients with high or relatively high urinary calcium and recurrent calcium stones. 1

• Effective dosing regimens include: 1

  • Hydrochlorothiazide 25 mg twice daily or 50 mg once daily
  • Chlorthalidone 25 mg once daily
  • Indapamide 2.5 mg once daily

• Potassium supplementation (citrate or chloride) is often needed to prevent hypokalemia 1

• Dietary sodium restriction must be continued to maximize hypocalciuric effect 1

• High-risk first-time stone formers may also benefit: Those with solitary kidney, hypertension, large stone burden, or refractory to other measures 1

Potassium Citrate (For Hypocitraturia)

Potassium citrate therapy should be offered to patients with recurrent calcium stones and low or relatively low urinary citrate. 1, 4

• FDA-approved indication: Management of hypocitraturic calcium oxalate nephrolithiasis 4
• Citrate acts as a potent inhibitor of calcium oxalate crystallization 1
• Patients with normal citrate but low urinary pH may also benefit 1

Dosing based on severity of hypocitraturia: 4

• Severe hypocitraturia (<150 mg/day): Start with 60 mEq/day (30 mEq twice daily or 20 mEq three times daily with meals)

• Mild to moderate hypocitraturia (>150 mg/day): Start with 30 mEq/day (15 mEq twice daily or 10 mEq three times daily with meals)

• Maximum studied dose is 100 mEq/day; higher doses should be avoided 4

• Treatment goal: Restore urinary citrate to >320 mg/day (ideally approaching 640 mg/day) and increase urinary pH to 6.0-7.0 4

• A Cochrane review demonstrated that citrate therapy significantly reduces new stone formation (RR 0.26,95% CI 0.10 to 0.68) and reduces stone size (RR 2.35,95% CI 1.36 to 4.05) 5

Monitoring and Follow-up

A single 24-hour urine specimen should be obtained within six months of initiating treatment to assess response to dietary and/or medical therapy. 1, 3

• After initial follow-up, annual 24-hour urine collection is recommended to assess adherence and metabolic response 1, 3
• More frequent monitoring may be needed based on stone activity 1

Periodic blood testing is mandatory for patients on pharmacological therapy: 1

• Thiazides: Monitor for hypokalemia and glucose intolerance
• Potassium citrate: Monitor for hyperkalemia
• Serum electrolytes, creatinine, and complete blood counts should be checked every four months 4

Repeat stone analysis should be obtained when available, especially in patients not responding to treatment, as stone composition may change. 1

Common Pitfalls and Caveats

• Do not restrict dietary calcium: This paradoxically increases stone risk by allowing more oxalate absorption 1
• Avoid calcium supplements unless specifically indicated: They increase stone risk compared to dietary sources 1
• Sodium restriction is critical: High sodium intake undermines both dietary and thiazide therapy 1
• Potassium citrate is contraindicated in hyperkalemia: Monitor serum potassium regularly 4
• Discontinue treatment if complications develop: Hyperkalemia, significant rise in creatinine, or fall in hemoglobin/hematocrit 4
• Main side effect of citrate therapy is gastrointestinal disturbance: This leads to higher dropout rates (RR 4.45,95% CI 1.28 to 15.50) 5

Special Populations

Patients with enteric hyperoxaluria require modified approach: 1

• More restrictive oxalate diets
• Higher calcium intakes (may include supplements with meals)
• Target urinary oxalate reduction in those with malabsorptive conditions

Conservative management for obstructing stones ≤6mm: 3, 6

• Medical expulsive therapy with alpha-blockers is first-line
• NSAIDs for pain management
• Maximum 4-6 weeks of conservative treatment
• Mandatory imaging follow-up