What is the current management of renal stones?

Current Management of Renal Stones

The management of renal stones requires a dual approach: initial evaluation with stone analysis and metabolic testing, followed by aggressive fluid intake (≥2.5 liters daily) combined with stone-specific dietary modifications and pharmacological therapy based on stone composition. 1, 2

Initial Evaluation and Diagnostic Workup

All patients with newly diagnosed kidney stones require:

• Detailed medical and dietary history focusing on fluid intake, protein consumption, calcium intake, sodium intake, and medications that may promote stone formation 1
• Serum chemistries including electrolytes, calcium, creatinine, and uric acid to identify underlying metabolic conditions 1
• Urinalysis with both dipstick and microscopic evaluation to assess urine pH and identify pathognomonic crystals 1, 2
• Stone analysis at least once when stone material is available, as composition (uric acid, cystine, struvite, calcium oxalate, calcium phosphate) directly determines treatment strategy 1, 2
• Imaging review to quantify stone burden; multiple or bilateral stones indicate higher recurrence risk 1, 2
• Serum intact parathyroid hormone if primary hyperparathyroidism is suspected (elevated or high-normal serum calcium) 1, 2

Metabolic Testing

Perform 24-hour urine collection in all recurrent stone formers and high-risk first-time formers (those with multiple stones, bilateral stones, nephrocalcinosis, or strong family history). 1, 2

• Analyze for: total volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 1, 2
• Two collections are preferred over one to account for day-to-day variability 1
• Add urinary cystine measurement if cystine stones are known or suspected, or with family history of cystinuria 1
• Suspect primary hyperoxaluria when urinary oxalate exceeds 75 mg/day in adults without bowel dysfunction 1

Dietary Management (Universal Recommendations)

Fluid intake is the single most critical intervention across all stone types:

• Target urine volume ≥2.5 liters daily through increased fluid intake 1, 2
• This represents a Standard recommendation with Grade B evidence 1
• Observational studies suggest coffee, tea, wine, and orange juice may reduce stone risk, while sugar-sweetened beverages increase risk 1

For calcium stones with hypercalciuria:

• Limit sodium intake to 2,300 mg daily (high sodium increases urinary calcium excretion) 1, 2
• Maintain normal dietary calcium intake of 1,000-1,200 mg/day (low calcium diets paradoxically increase stone risk by increasing oxalate absorption) 1, 2
• This represents a Standard recommendation with Grade B evidence 1

For cystine stones:

• Target even higher fluid intake (≥4 liters daily) to decrease urinary cystine concentration below 250 mg/L 2
• Restrict sodium and protein intake 1, 2

Pharmacological Management by Stone Type

Calcium Stones

For hypercalciuria:

• Thiazide diuretics are first-line therapy combined with continued dietary sodium restriction 2
• Monitor for hypokalemia and glucose intolerance 1, 2

For hypocitraturia:

• Potassium citrate therapy to increase urinary citrate (target ≥400 mg/day) and raise urinary pH 1, 2, 3
• Dosing: Start 30 mEq/day for mild-moderate hypocitraturia (citrate >150 mg/day) or 60 mEq/day for severe hypocitraturia (citrate <150 mg/day) 3
• Take with meals or within 30 minutes after meals 3
• Maximum studied dose is 100 mEq/day 3

Uric Acid Stones

First-line therapy is urinary alkalinization, not uric acid reduction:

• Potassium citrate to raise urinary pH to approximately 6.0 enhances uric acid solubility 1, 2, 3
• Do NOT routinely offer allopurinol as first-line therapy because most patients have low urinary pH rather than hyperuricosuria as the primary problem 1
• Allopurinol will not prevent stones in those with unduly acidic urine 1

Cystine Stones

Stepwise approach:

1. First-line: Increased fluid intake (≥4 liters daily), sodium and protein restriction, and urinary alkalinization with potassium citrate to raise pH to approximately 7.0 1, 2
2. Second-line: If modifications are insufficient or large recurrent stone burden exists, offer tiopronin (alpha-mercaptopropionylglycine), a cystine-binding thiol drug 1, 2
3. Tiopronin is more effective and has fewer adverse events than d-penicillamine 1

Struvite Stones

Monitor for reinfection as these are infection stones requiring urease inhibitors like acetohydroxamic acid (AHA), though extensive side effects limit use 1

Surgical Management Considerations

Preoperative requirements:

• Obtain non-contrast CT prior to percutaneous nephrolithotomy (PCNL) - Strong recommendation 1
• Obtain urinalysis prior to any intervention 1
• Obtain urine culture if infection is suspected based on urinalysis or clinical findings; treat with appropriate antibiotics before intervention 1

Treatment selection depends on patient- and stone-specific factors including size, location, composition, and stone burden 1

Follow-Up Monitoring

Initial follow-up:

• Obtain single 24-hour urine specimen within 6 months of initiating treatment to assess response to dietary/medical therapy 1, 2
• Measure urinary citrate and/or pH to determine adequacy of dosage 3

Ongoing monitoring:

• Annual 24-hour urine specimens thereafter, or more frequently depending on stone activity, to assess adherence and metabolic response 1, 2
• Periodic blood testing to assess for adverse effects of pharmacological therapy (e.g., hypokalemia with thiazides, hyperkalemia with potassium citrate, elevated liver enzymes with allopurinol or tiopronin, anemia with AHA or tiopronin) 1, 2
• Repeat stone analysis when available, especially in patients not responding to treatment, as stone composition may change 1, 2

Common Pitfalls to Avoid

• Do not restrict dietary calcium in calcium stone formers; this paradoxically increases oxalate absorption and stone risk 1, 2
• Do not use allopurinol as first-line for uric acid stones; alkalinization addresses the primary defect (low pH) 1
• Do not discontinue monitoring once stones resolve; longitudinal follow-up identifies patients becoming refractory to therapy 1
• Do not ignore medication side effects; regular blood testing prevents serious complications 1, 2