Likelihood of Spontaneous Renal Stone Passage by Size
Stones <5 mm pass spontaneously in 68-75% of cases overall, with distal ureteral stones <5 mm achieving passage rates up to 89%, while stones ≥5 mm drop to 47-62% passage rates, and stones >10 mm rarely pass without intervention. 1, 2, 3
Size-Specific Passage Rates
Stones <5 mm
- Overall spontaneous passage: 68-75% 1, 3
- Distal ureteral location: 89% 1, 3
- Mid-ureteral location: 58-70% 1
- Upper ureteral location: 49-75% 1, 3
- Mean time to passage: 17 days (range 6-29 days) 1
Stones 5-10 mm
- Overall spontaneous passage: 47-62% 1, 2, 3
- Passage rates decline significantly as size increases within this range 1
- Research data shows more granular breakdown: 65% for 5 mm stones, 33% for 6 mm stones, and only 9% for stones ≥6.5 mm 4
Stones >10 mm
- Spontaneous passage is unlikely and surgical intervention is typically required 2, 3, 5
- The European Association of Urology recommends active intervention for stones >10 mm due to low spontaneous passage rates 3
Location-Based Passage Rates
Stone location significantly impacts passage probability, with distal stones having the highest success rates: 1, 4, 6
The more proximal the stone location, the lower the chance of spontaneous passage, independent of size 6
Time Course of Passage
Most stones that will pass spontaneously do so within the first 4 weeks: 1, 6
- 55.3% pass within 7 days 6
- 73.7% pass within 14 days 6
- 88.5% pass within 28 days 6
- 97.7% pass within 60 days 6
Medical Expulsive Therapy Impact
Alpha-blockers (tamsulosin 0.4 mg daily) increase passage rates by an absolute 22-29% for stones 5-10 mm: 3, 5
- With alpha-blockers: 77-87% passage rate 3, 5
- Without alpha-blockers: 54-61% passage rate 3, 5
- Number needed to treat: 4-5 patients 3
- Reduces time to expulsion by approximately 3 days 3
Clinical Decision Algorithm
Conservative Management Appropriate When:
- Stone size ≤5 mm (75% passage rate justifies observation) 1, 3
- Stone size 5-10 mm with distal location (consider MET to increase passage to 77%) 2, 5
- Well-controlled pain without excessive analgesic requirements 5
- No clinical evidence of sepsis or infection 5
- Adequate renal functional reserve 5
Active Intervention Indicated When:
- Stone size >10 mm (passage unlikely) 2, 3, 5
- Failed conservative management after 4-6 weeks 3
- Complications develop (infection, refractory pain, declining renal function) 1, 3
- Stone growth on serial imaging 1
Important Caveats
The 6 mm threshold represents a critical decision point where passage rates drop dramatically from 65% at 5 mm to 33% at 6 mm and only 9% at 6.5 mm or larger 4. This sharp decline should inform aggressive consideration of intervention for stones approaching or exceeding 6 mm.
Renal stones have lower passage rates than ureteral stones of equivalent size because they must first enter the ureter before passage can occur 6, 7. Spontaneous passage of renal stones occurs in only 3-29% of cases 1.
Hydronephrosis presence may predict lower passage rates in specific subgroups, though stone size and location remain the dominant predictors 4, 8.