What is the typical time frame for passing kidney stones?

Typical Time Frame for Passing Kidney Stones

Most kidney stones smaller than 5mm will pass spontaneously within 17 days (range 6-29 days), with approximately 75% of these stones passing without intervention. 1

Factors Affecting Stone Passage Time

Stone Size

• <5mm stones: 75% pass spontaneously, typically within 17 days 1
• ≥5mm stones: 62% pass spontaneously 1
• Passage rates by specific size:
  • 0-2mm: 98% pass spontaneously within 20 weeks 2
  • 3mm: 98% pass spontaneously within 20 weeks 2
  • 4mm: 81% pass spontaneously within 20 weeks 2
  • 5mm: 65% pass spontaneously within 20 weeks 2
  • 6mm: 33% pass spontaneously within 20 weeks 2
  • ≥6.5mm: only 9% pass spontaneously within 20 weeks 2

Stone Location

• Upper ureteral stones: 49-52% pass spontaneously 1
• Mid-ureteral stones: 58-70% pass spontaneously 1
• Distal ureteral stones: 68-83% pass spontaneously 1
• Location-specific passage rates:
  • Distal stones <5mm: 89% pass spontaneously 1
  • Upper ureteral stones <5mm: 75% pass spontaneously 1

Time to Passage by Size

For 95% of stones to pass spontaneously 3:

• ≤2mm stones: approximately 31 days
• 2-4mm stones: approximately 40 days
• 4-6mm stones: approximately 39 days

Medical Expulsive Therapy (MET)

Alpha-blockers like tamsulosin can facilitate stone passage for ureteral stones by relaxing smooth muscle in the ureter 4. This therapy should be considered for stones that have a reasonable chance of spontaneous passage but may benefit from expedited transit.

When to Consider Intervention

Consider active intervention in these scenarios:

• Stones >6mm (only 9-33% pass spontaneously) 2
• Persistent symptoms despite adequate pain control
• Evidence of infection or obstruction
• Stones not progressing after 4-6 weeks of observation

Follow-up Recommendations

• Follow-up imaging (ultrasound or KUB X-ray) within 1-2 weeks to assess stone position 4
• Increase fluid intake to >2L/day to help prevent recurrence 4
• Consider strain urine to capture passed stones for analysis

Common Pitfalls to Avoid

1. Assuming all stones require intervention: Most small stones (<5mm) will pass spontaneously within 2-4 weeks 1
2. Inadequate follow-up: Even small stones can cause complications if they don't pass
3. Misinterpreting stone passage time: The passage of a pre-existing stone after implementing dietary changes doesn't mean the intervention was ineffective 1
4. Overlooking metabolic evaluation: Consider metabolic workup for patients with recurrent stones 4

Special Considerations

• Approximately 20% of asymptomatic renal stones ≤5mm may eventually require surgical intervention within 5 years 5
• Younger age (≤50 years) and history of stone surgery are significant predictors of requiring intervention, even more so than stone size 5
• Stone recurrence rates may be as high as 30-50% after 5 years without preventive measures 1

Understanding these timeframes helps set appropriate expectations for patients and guides clinical decision-making regarding when to continue observation versus when to consider intervention.