Ureteral Stone Size and Spontaneous Passage
Ureteral stones ≤5 mm in diameter have a high likelihood of spontaneous passage (approximately 68%), while stones >5 mm have a significantly lower chance of passing without intervention (approximately 47%). 1
Stone Size and Passage Rates
The likelihood of spontaneous passage is strongly correlated with stone size:
- ≤5 mm stones: 68% spontaneous passage rate (95% CI: 46-85%) 1
- >5 mm to ≤10 mm stones: 47% spontaneous passage rate (95% CI: 36-59%) 1
More detailed breakdown of passage rates by specific size:
- 0-2 mm: 98% passage rate 2
- 3 mm: 98% passage rate 2
- 4 mm: 81% passage rate 2
- 5 mm: 65% passage rate 2
- 6 mm: 33% passage rate 2
- ≥6.5 mm: 9% passage rate 2
Factors Affecting Stone Passage
Stone Location
- Distal ureteral stones have higher passage rates than proximal stones 2, 3
- Right-sided stones pass more readily than left-sided stones 3
Time to Stone Passage
- <2 mm: Average 6.8 days 3
- 2-4 mm: Average 12.6 days 3
- 4-6 mm: Average 14.8 days 3
- 6-8 mm: Average 21.8 days 3
Cumulative passage rates over time:
- 55.3% pass within 7 days
- 73.7% pass within 14 days
- 88.5% pass within 28 days
- 97.7% pass within 60 days 3
Management Recommendations
For uncomplicated ureteral stones:
- ≤10 mm: Observation should be offered 1
- ≤10 mm distal stones: Medical expulsive therapy (MET) with α-blockers should be offered 1
Important Caveats
Pediatric patients: Children show similar passage rates for ureteral stones up to 5 mm, but stones >5 mm rarely pass spontaneously in any age group 4, 5
Intervention thresholds: Intervention may be required in approximately 50% of ureteral calculi >5 mm 6
Observation period: For stones likely to pass spontaneously, observation for up to 40 days may be reasonable before intervention 6
Urgent drainage: Urgent drainage with stent or percutaneous nephrostomy is mandatory for obstructing stones with suspected infection 7
Conclusion
Stone size and location are the most important predictors of spontaneous passage. The 5 mm threshold represents an important clinical decision point, with significantly lower passage rates for stones larger than this size. For stones ≤10 mm, observation with or without medical expulsive therapy is appropriate, while recognizing that stones >5 mm have substantially lower spontaneous passage rates.