Can a 4 mm kidney stone pass through the ureters?

Can a 4 mm Kidney Stone Pass Through the Ureters?

Yes, a 4 mm ureteral stone has a high likelihood of spontaneous passage (approximately 81% within 20 weeks), and observation with or without medical expulsive therapy should be offered as first-line management in patients with controlled symptoms. 1, 2

Spontaneous Passage Rates by Stone Size

The evidence clearly demonstrates that stone size is the strongest predictor of spontaneous passage:

• Stones ≤5 mm: Approximately 68% spontaneous passage rate (95% CI: 46-85%) 1
• 4 mm stones specifically: 81% spontaneous passage rate within 20 weeks 2
• Stones >5 mm but ≤10 mm: 47% spontaneous passage rate (95% CI: 36-59%) 1
• Stones >10 mm: Unlikely to pass spontaneously and typically require surgical intervention 1

Initial Management Approach

For uncomplicated 4 mm ureteral stones, observation with or without medical expulsive therapy (MET) using alpha-blockers is appropriate as initial management. 3, 1

Prerequisites for Conservative Management:

• Well-controlled pain 3
• No clinical evidence of sepsis 3
• Adequate renal functional reserve 3
• No anatomical abnormalities complicating passage 4

Medical Expulsive Therapy:

• Alpha-blockers increase stone passage rates by approximately 29% compared to control (95% CI: 20-37%) 1
• Patients must be counseled about off-label use and potential side effects 3

Time Frame and Monitoring

Conservative therapy should be limited to a maximum of 6 weeks from initial presentation to avoid irreversible kidney injury. 3, 1

Expected Passage Timeline:

• For stones 2-4 mm: Average time to passage is 12.2 days 5
• For 95% of stones 2-4 mm to pass: Up to 40 days may be required 5

Required Monitoring:

• Periodic imaging studies to monitor stone position 3
• Assessment for hydronephrosis 3
• CT scan is superior to ultrasound for accurate stone size determination 4, 1

Factors Affecting Passage Success

Beyond size, several factors influence spontaneous passage rates 2, 5:

• Location: Distal ureteral stones have higher passage rates than proximal stones 1, 5
• Side: Right-sided stones pass more readily than left-sided 5
• Hydronephrosis severity: Severe hydronephrosis predicts lower passage rates 6
• Inflammatory markers: Neutrophil-to-lymphocyte ratio ≥3.14 correlates with retained stones 6

When to Intervene

Surgical intervention (ureteroscopy or shock wave lithotripsy) should be offered if: 3

• Stone fails to pass after 6 weeks of observation 3, 1
• Intractable pain despite adequate analgesia 4
• Evidence of urinary tract infection with obstruction 3, 4
• Progressive or severe hydronephrosis 3
• Patient preference for definitive treatment 3

Common Pitfalls

• Underestimating passage time: While average passage is ~12 days, some 4 mm stones may take up to 40 days 5
• Inadequate follow-up: Failure to monitor with periodic imaging can miss complications like progressive hydronephrosis 3
• Ignoring infection: Untreated bacteriuria with obstruction can lead to urosepsis 3
• Prolonged conservative management: Exceeding 6 weeks risks irreversible kidney damage 3, 1

Special Populations

Pediatric Patients:

• Observation with or without MET is appropriate for stones ≤10 mm 3
• Stone-free rates of 62% for stones <5 mm in distal ureter 3, 1

Pregnant Patients:

• Observation is first-line therapy with well-controlled symptoms 3
• Spontaneous passage rates similar to non-pregnant patients 3
• Coordinate any intervention with obstetrics 3