Will Nonobstructing Kidney Stones Pass?
Yes, most nonobstructing kidney stones will pass spontaneously, but the likelihood depends critically on stone size and location—stones <5 mm pass in 68-89% of cases, while stones 5-10 mm pass in only 47-62% of cases. 1
Stone Passage Rates by Size and Location
Stones <5 mm
- Spontaneous passage occurs in 68-75% of cases overall 1
- Distal ureteral stones <5 mm pass in 89% of cases 1
- Upper ureteral stones <5 mm pass in 75% of cases 1
- Average time to passage is 8-17 days 1, 2
- For 95% of stones ≤2 mm to pass, it takes approximately 31 days 2
Stones 5-10 mm
- Spontaneous passage drops to 47-62% overall 1
- Distal stones 5-10 mm have higher passage rates than proximal stones 1
- Average time to passage extends to 12-40 days depending on exact size 2
- Medical expulsive therapy with alpha-blockers increases passage rates by an absolute 22-29% 3
Stones >10 mm
- Spontaneous passage is unlikely and intervention should be considered 1, 3
- These stones have low passage rates and high complication risk 3
Location-Specific Passage Rates
Stone location significantly predicts spontaneous passage and symptom development: 4, 2
- Distal ureteral stones: 68-83% passage rate 1
- Mid ureteral stones: 58-70% passage rate 1
- Upper ureteral stones: 49-52% passage rate 1
- Lower pole renal stones are significantly less likely to pass (2.9%) compared to upper/mid pole stones (14.5%) 4
Natural History of Nonobstructing Renal Stones
For asymptomatic nonobstructing renal calculi managed with observation: 4
- Most (72%) remain asymptomatic through average 3+ year follow-up 4
- Less than 30% develop renal colic 4
- Only 7% pass spontaneously 4
- Upper/mid pole stones are more likely to become symptomatic (40.6%) than lower pole stones (24.3%) 4
Critical Pitfall: Silent Obstruction
A small but important subset (2-3%) of asymptomatic nonobstructing stones can cause painless silent obstruction requiring intervention after an average of 37 months. 4 This underscores the need for regular follow-up imaging even in asymptomatic patients to prevent renal loss.
Medical Expulsive Therapy Considerations
For distal ureteral stones 5-10 mm, tamsulosin 0.4 mg daily increases stone passage rates to 81-87% compared to 61-79% with placebo. 3
- Number needed to treat is 4-5 patients 3
- Reduces time to stone expulsion by approximately 3 days 3
- Should be discontinued if infection, refractory pain, or declining renal function develops 1, 3
- Maximum conservative management period is 4-6 weeks to avoid irreversible kidney injury 1, 3
When Observation is Inappropriate
Observation alone is inappropriate for nonobstructing stones when: 1
- Stone demonstrates growth on serial imaging 1
- Patient has high risk of stone formation 1
- Infection or sepsis is present 1, 3
- Declining renal function occurs 1, 3
- Refractory pain despite adequate analgesia 1, 3
Intervention Thresholds
Active intervention should be offered when: 1