Kidney stones smaller than 10 mm are found more and more often, and a common question follows: does a stone this small need treatment at all, or should it simply be watched? At the Emirates Urological Society conference in 2025, this was the subject of a debate. The motion was whether all kidney stones under 10 mm should be managed conservatively first, meaning monitored with regular check-ups instead of removed.
I argued the interventional side: that earlier treatment can prevent complications and stop stones coming back. This post sets out that case, and also where I think the evidence actually leaves us.
Why the question matters more each year
Each year brings new record temperatures. A warming world could lead to more urinary stones than before, and as more stones are diagnosed, more patients and doctors face this decision about small ones.
Evidence that small stones do not always stay quiet
The strongest point for my side came from a randomised controlled trial, the kind of study where patients are assigned to one approach or the other by chance. Published by Sorensen and colleagues in the New England Journal of Medicine in 2022, it looked at patients already having surgery for a stone in the ureter (the tube from the kidney to the bladder) or in the other kidney.
When small stones that were causing no symptoms were also removed during that surgery, relapse was less common than when they were left behind. The number of emergency department visits related to the surgery was similar in both groups. Leaving small, silent stones untreated was linked to a higher relapse rate.
A 2019 systematic review by Han and colleagues, which pooled studies of patients whose silent kidney stones were watched over time, showed how unpredictable these stones can be. Across the studies, spontaneous passage ranged from 3% to 29%. Symptoms developed in 7% to 77%, the stone grew in 5% to 66%, and surgery was eventually needed in 7% to 26%.
Pain from a small stone is real
A small Scandinavian study published in 1993 by Brandt and colleagues looked at patients with unexplained flank pain or repeated urinary infections who had small stones in a calyx (one of the cup-shaped chambers inside the kidney) that were not blocking the flow of urine. When the stones were removed, whether by keyhole surgery, shock wave treatment, ureteroscopy or open surgery, most patients were relieved of their symptoms. Where the stone stayed unchanged, the symptoms stayed too.
The authors concluded that small calyceal stones can cause pain, and that treating one is justified in a patient with flank pain and no other apparent cause.
The evidence for watching is real too
A fair debate has to present the other side, and my slides did. Current guidelines on watching kidney stones lack support from high-quality studies. The same 2019 review found no link between how long patients were watched and how often they needed surgery. Only a minority in each group needed an operation, which supports clinical judgment guiding some patients towards active surveillance.
A prospective study by Inci and colleagues in 2007 followed patients with silent stones in the lower part of the kidney. About one in three had disease progression, and a third of those needed treatment in the long term. The authors suggested yearly monitoring for silent lower pole stones under 10 mm, with shorter intervals if the stone grows, and said patients should be told about the 33% rate of progression.
A 2021 review by Lovegrove and colleagues, covering 25 years of follow-up, found that stone size alone did not reliably predict symptoms. The risk of needing treatment was higher for stones over 5 mm than under 5 mm, and over 10 mm than under 10 mm. Stones that are growing and larger than 5 mm are recommended for treatment.
Fragments left behind after treatment behave in a similar way. A systematic review and meta-analysis found that around a third of patients with dust or fragments of 4 mm or less had progression and needed another procedure within three years, while about a third passed them naturally within two years. For fragments over 4 mm, the few studies available suggest they rarely pass on their own and often need treatment.
Where I land: patient by patient
The European Association of Urology guideline for 2025 states that it is still debatable whether kidney stones should be treated, or whether yearly follow-up is enough for silent calyceal stones that have stayed stable for six months. It lists stone growth, new blockage, associated infection, and sudden or long-lasting pain as reasons to treat.
So my conclusion was that these decisions should be made case by case. A personalised approach is best. For stones under 10 mm, I would consider active treatment when there is stone growth, pain or blood in the urine, blockage of the kidney, urinary infection or a matrix stone (a soft stone made mostly of protein), or a cystine stone (a rare type caused by an inherited condition).
Treatment also makes sense for patients at high risk of forming more stones, and when the patient prefers it. Other illnesses count too, as do social circumstances such as a person's profession or travel requirements.
If you have a kidney stone or symptoms such as flank pain or blood in the urine, please see a urologist to discuss whether watching or treatment is right for you.