When do kidney stones require medical intervention?

When Kidney Stones Require Intervention

Kidney stones require intervention when they are >10 mm in diameter, cause obstruction with infection, persistent pain, or renal impairment, or when they are unlikely to pass spontaneously based on size and location. 1

Indications for Intervention

Stone Size and Location

• <5 mm stones: Generally pass spontaneously (observation with medical expulsive therapy is appropriate)
• 5-10 mm stones: May require intervention as up to 50% will not pass spontaneously
• >10 mm stones: Almost always require intervention as they are unlikely to pass spontaneously 1, 2

Urgent/Emergency Intervention Required

• Obstructing stones with signs of infection or sepsis
• Complete obstruction with acute renal failure
• Intractable pain not responsive to analgesics
• Solitary kidney with obstruction 1, 3

Elective Intervention Considerations

• Persistent symptoms despite conservative management
• Stones unlikely to pass based on size/location
• Patient preference after failed observation
• High-risk stone composition (e.g., infection stones, cystine stones)
• Anatomic abnormalities that increase risk of obstruction 1, 4

Evaluation Before Intervention

1. Imaging:

   • Non-contrast CT scan is gold standard (detects >99% of stones)
   • Determines stone size, location, and degree of obstruction 1, 4

2. Laboratory Testing:

   • Urinalysis and urine culture (to identify infection)
   • CBC and platelet count (if significant risk of hemorrhage)
   • Serum electrolytes and creatinine (to assess renal function)
   • Stone analysis (when available) 1

3. Metabolic Evaluation:

   • 24-hour urine collection for high-risk or recurrent stone formers
   • Serum intact parathyroid hormone if hyperparathyroidism suspected 1

Intervention Options Based on Clinical Scenario

For Ureteral Stones

• ≤10 mm distal ureteral stones:

  • First: Observation with medical expulsive therapy (α-blockers)
  • If unsuccessful after 4-6 weeks: URS or SWL 1

• >10 mm ureteral stones:

  • Direct intervention with URS or SWL recommended 1

For Renal Stones

• ≤10 mm lower pole stones:

  • Observation may be appropriate if asymptomatic
  • Otherwise, SWL or URS 1

• >10 mm lower pole stones:

  • PCNL or URS recommended 1

• >20 mm total renal stone burden:

  • PCNL is first-line treatment 1

Special Populations

1. Patients on anticoagulation/antiplatelet therapy:

   • URS is first-line therapy (safer than SWL or PCNL) 1

2. Pediatric patients:

   • For ureteral stones ≤10 mm: Observation with/without MET
   • For stones that fail observation: URS or SWL 1

3. Infected stones:

   • Complete stone removal is essential
   • If purulent urine is encountered during intervention, abort procedure, establish drainage, and continue antibiotics 1, 3

Important Considerations

• Residual fragments: Should be addressed, especially if infection stones are suspected, as 43% of patients with residual fragments experience stone-related events 1

• Failed SWL: If initial SWL fails, endoscopic therapy (URS or PCNL) should be offered as next treatment option 1

• Safety during procedures: Safety guidewire should be used for most endoscopic procedures 1

• Follow-up: Imaging should be performed 4-6 weeks after intervention to confirm stone clearance 4

Prevention of Recurrence

• Increase fluid intake to achieve urine volume of at least 2.5 liters daily
• Dietary modifications based on stone composition
• Medications based on metabolic abnormalities (thiazides, potassium citrate, allopurinol) 1

Common Pitfalls to Avoid

1. Delaying intervention for obstructing stones with signs of infection (urologic emergency)
2. Attempting blind stone extraction (risk of ureteral injury)
3. Failing to obtain stone analysis when available
4. Not addressing residual fragments after intervention
5. Neglecting metabolic evaluation in recurrent stone formers 1, 4