Observation & active surveillance

Two very different clinical situations

Observation means quite different things depending on whether the stone is sitting in the kidney or moving down the ureter.

1. Small ureteric stones expected to pass

Most ureteric stones smaller than about 5 mm - and many up to 7 mm - will pass on their own within four to six weeks, particularly if they have already travelled into the lower ureter. The published estimates are:^{1, 2}

• Stones < 5 mm - approximately 75-90% spontaneous passage.
• Stones 5-7 mm - approximately 45-60%.
• Stones > 7 mm - approximately 25-30%.

Observation is appropriate only if the pain is controlled, the kidney is not severely obstructed, there is no infection, and kidney function is preserved.

2. Asymptomatic kidney stones

Small stones inside the kidney that are causing no symptoms and no obstruction can often be watched rather than treated. Guidelines support active surveillance for selected non-obstructing calyceal stones, particularly < 10 mm, in patients without high-risk features.¹

This approach must be weighed against the possibility of the stone enlarging, migrating into the ureter and causing pain, or causing infection. For some patients - pilots, long-haul truck drivers, or those with a solitary kidney - pre-emptive treatment may be preferred.

When observation is not the right answer

• Obstructed kidney with fever or infection - this is an emergency.
• Pain that cannot be controlled with oral analgesics.
• Solitary kidney with any obstructing stone.
• Declining kidney function.
• Stone > 7-10 mm in the ureter (low chance of passage).
• Patient in an occupation where sudden severe pain is unacceptable (pilot, professional driver).
• Pregnancy with persistent symptoms.

How observation is managed safely

1. Confirm the stone and rule out red flags

   CT KUB to confirm stone position, size, and any hydronephrosis. Urine culture to exclude infection. Blood tests for kidney function.

2. Pain plan

   Simple analgesia (paracetamol plus an NSAID such as diclofenac where safe) is the foundation. Short courses of opioids are occasionally added. Alpha-blockers (MET) may be used for selected distal ureteric stones.

3. Fluid target

   Aim for a urine output of around 2.5 L a day.

4. Safety-netting

   Clear instructions on what to look out for - fever, uncontrolled pain, passing no urine - and a defined route back into the system if things change.

5. Follow-up imaging

   Usually a plain KUB x-ray or ultrasound at 2-4 weeks to check passage. For kidney stones on active surveillance, repeat imaging (ultrasound or low-dose CT) every 6-12 months.

6. Review threshold

   If the stone has not passed at 4-6 weeks, or grows/obstructs on surveillance, definitive treatment is arranged.

Related pages

References

1. Skolarikos A, et al. EAU Guidelines on Urolithiasis. 2025.
2. Kasivisvanathan V, et al. Cohort studies on spontaneous passage of ureteric stones by size.