Management of Non-obstructing Kidney Stones
Active surveillance is the recommended first-line approach for asymptomatic, non-obstructing kidney stones up to 15 mm in size, with regular follow-up imaging to monitor for stone growth, development of symptoms, or silent obstruction. 1, 2
Initial Assessment and Surveillance Protocol
Screening evaluation should include:
Follow-up imaging is essential during active surveillance to detect:
- Stone growth
- Development of hydronephrosis
- Silent obstruction (occurs in approximately 2-3% of cases) 3
Indications for Intervention in Non-obstructing Stones
Active surveillance should be discontinued and intervention considered when:
- Stone growth is detected on follow-up imaging
- Associated infection develops
- Symptoms develop (pain, hematuria)
- Vocational reasons necessitate treatment (e.g., pilots, frequent travelers)
- Patient preference for definitive treatment 1
Treatment Options When Intervention Is Indicated
Treatment selection depends on stone size and location:
| Stone Size | Stone Location | Recommended Treatment |
|---|---|---|
| <10 mm | Renal pelvis or upper/middle calyx | SWL or flexible URS |
| 10-20 mm | Renal pelvis or upper/middle calyx | SWL or flexible URS |
| <10 mm | Lower pole | fURS or SWL |
| 10-20 mm | Lower pole | fURS or PCNL |
| >20 mm | Any location | PCNL |
SWL = Shock Wave Lithotripsy; URS = Ureteroscopy; fURS = flexible Ureteroscopy; PCNL = Percutaneous Nephrolithotomy 1, 2
Preventive Measures During Active Surveillance
Hydration
- Maintain fluid intake of 3.5-4 liters daily to produce at least 2-2.5 liters of urine 2
Dietary Modifications
- Maintain normal dietary calcium intake (1,000-1,200 mg/day)
- Reduce sodium intake to <2,300 mg/day
- Limit intake of foods very high in oxalate
- Increase intake of fruits and vegetables 2
Medication Therapy (based on stone composition)
- Calcium stones: Thiazide diuretics for hypercalciuria
- Uric acid stones: Allopurinol for hyperuricosuria
- All stone types: Potassium citrate (0.1-0.15 g/kg daily) to increase urinary pH and citrate levels 2
Natural History of Non-obstructing Stones Under Surveillance
Long-term studies show:
- Most stones (>70%) remain asymptomatic through an average follow-up of more than 3 years
- Approximately 28% cause symptoms during follow-up
- Only about 7% pass spontaneously
- Lower pole stones are significantly less likely to cause symptoms or pass spontaneously compared to upper/mid pole stones 3
Important Caveat
Silent hydronephrosis suggesting obstruction can occur in approximately 3% of cases, highlighting the importance of regular follow-up imaging to prevent renal damage 3. This risk, while small, underscores the need for adherence to surveillance protocols.
Special Considerations
- Stone analysis should be performed at least once to guide preventive measures 2
- Metabolic evaluation is recommended for high-risk patients and all recurrent stone formers 1, 2
- Complete stone removal is essential when intervention is performed to prevent further stone growth and complications 2
By following this evidence-based approach to non-obstructing kidney stones, clinicians can minimize unnecessary interventions while ensuring appropriate treatment when indicated, ultimately reducing morbidity and preserving renal function.