What are the odds of a 6mm ureteral stone passing spontaneously without intervention?

Spontaneous Passage Rate for 6mm Ureteral Stones

A 6mm ureteral stone has approximately a 33% chance of passing spontaneously without intervention, though this varies significantly by location—distal stones pass more frequently than proximal stones. 1

Stone Size-Specific Passage Rates

The evidence consistently demonstrates that 6mm stones fall into a transitional zone where spontaneous passage becomes substantially less likely:

• Stones 5-10mm: Overall spontaneous passage rate of approximately 47% (95% CI: 36-59%) 2
• Stones 6mm specifically: Passage rate of 33% in 20 weeks 1
• Stones >5mm: Passage rate of approximately 62% across all locations 3

For comparison, smaller stones have markedly higher passage rates: stones ≤5mm pass spontaneously in 68% of cases (95% CI: 46-85%), while stones <5mm pass in 75% of cases 2, 3

Location Matters Critically

Stone location is the second most important predictor after size 4, 1:

• Distal ureter: 68% overall passage rate 3
• Mid ureter: 58% overall passage rate 3
• Proximal ureter: 49% overall passage rate 3

The more proximal the stone location and the larger the size beyond 6mm, the less likely spontaneous passage becomes 4

Time Frame for Passage

If a 6mm stone is going to pass spontaneously, expect a prolonged observation period 5, 4:

• Mean time to passage: 21.8 days for stones 6-8mm 4
• 95% passage window: Up to 39-40 days for stones 4-6mm 5
• Cumulative rates: 55.3% pass by 7 days, 73.7% by 14 days, 88.5% by 28 days, 97.7% by 60 days (for all stone sizes combined) 4

Clinical Management Approach

Conservative management with medical expulsive therapy (MET) is reasonable for 6mm stones as initial treatment, but patients must understand the relatively low success rate and need for close monitoring. 2

Requirements for Conservative Management:

• Well-controlled pain without excessive analgesic requirements 2
• No clinical evidence of sepsis or infection 2
• Adequate renal functional reserve 2
• Periodic imaging to monitor stone position and assess for hydronephrosis 2

Medical Expulsive Therapy:

Alpha-blockers increase stone passage rates by approximately 29% (95% CI: 20-37%) compared to observation alone 2. For distal ureteral stones <10mm, alpha-blockers achieve 77.3% stone-free rates versus 54.4% with placebo (OR 3.79,95% CI 2.84-5.06) 2

Time Limits for Conservative Management:

Limit conservative therapy to a maximum of 6 weeks from initial presentation to avoid irreversible kidney injury 6. Approximately 13.7% of patients require intervention due to symptom relapse or renal deterioration 4

When to Proceed with Intervention

For stones >10mm, surgical intervention is typically required as spontaneous passage is unlikely 2, 6. While 6mm stones technically fall below this threshold, their borderline size means many will ultimately require intervention 4:

• Ureteroscopy (URS): Stone-free rate of 93% for distal stones >10mm, 78% for mid-ureter stones >10mm 2
• Shock wave lithotripsy (SWL): Stone-free rate of 74% for distal stones >10mm, 76% for mid-ureter stones >10mm 2

URS yields significantly higher stone-free rates but has higher complication rates (3-6% ureteral injury) compared to SWL 2

Common Pitfalls

• Overestimating passage likelihood: Many clinicians assume stones <10mm will pass, but 6mm stones have only a 33% passage rate 1
• Prolonged observation without monitoring: Failure to perform periodic imaging can miss progressive hydronephrosis and renal deterioration 2
• Ignoring stone location: A 6mm proximal stone has substantially lower passage rates than a 6mm distal stone 3, 4
• Inadequate pain control: Patients with poorly controlled pain should not continue conservative management 2