Watching Feasible for Asymptomatic Kidney Stones

Dr Kevin Stritt

Many patients with asymptomatic renal stones can qualify for an active surveillance program, Swiss researchers report at the American Urological Association (AUA) 2023 Annual Meeting.

Kevin Stritt, MD, chief resident in the Urology Department at Lausanne University Hospital, said kidney stones often pass without symptoms. But until now, data on the frequency of asymptomatic, spontaneous passage of stones have been lacking.

The new data come from the NOSTONE trial, a prospective, multicenter, double-blind, placebo-controlled randomized trial to assess the efficacy of hydrochlorothiazide in the prevention of recurrence in patients with recurrent calcium-containing kidney stones.

Stritt and colleagues evaluated the natural history of asymptomatic renal stones during a median follow-up of 35 months. “We found for the first time that a relevant number of kidney stone passages [39%] were asymptomatic, spontaneous stone passages,” Stritt told Medscape Medical News.

All asymptomatic spontaneous stone passages were analyzed in a comparison of the total number of kidney stones on low-dose, nonintravenous contrast CT imaging at the beginning and end of the 3-year follow-up.

Of the 403 stones passed spontaneously, 61% (245) were symptomatic stone passages and 39% (158) were asymptomatic stone passages, Stritt told Medscape Medical News.

Asymptomatic stones were a median size of 2.4 mm, and symptomatic stones were 2.15 mm, which was not significantly different (P = .366), according to the researchers. Stritt said the spontaneous passage of asymptomatic stones was largely influenced by a higher number of stones on CT imaging at randomization (P = .001) and a lower total stone volume (P = .001).

Ephrem Olweny, MD, an assistant professor of urology and section chief of endourology at Rush University Medical Center, in Chicago, Illinois, said previous studies have found that the rate of spontaneous passage of kidney stones ranges from 3% to 29%.

“But this secondary analysis of data from a prior multicenter prospective randomized trial offers higher quality data that will be of value in guiding patient counseling,” Olweny said.

“Observation should be initially offered to these patients. However, patients should be informed that 52% are likely to develop symptoms, and some may indeed opt for pre-emptive surgical removal,” he added.

Dr David Schulsinger

David Schulsinger, MD, an associate professor in the Department of Urology at Stony Brook University Hospital, New York, said the incidence of kidney stones has been increasing worldwide, affecting approximately 12% of men and 6% of women. Dehydration and diets high in sodium and calcium are major factors, he said.

Patients with a history of stones have a 50% risk of recurrence in the next 5 years, and an 80% risk in their lifetime, he added.

Schulsinger said the message from the Swiss study is that urologists can be “comfortable” watching small stones, those averaging 2.4 mm or less in size. “But if a patient has a 7- or  8-mm stone, you might be more inclined to manage that patient a little bit more aggressively.”

Roughly half of patients with stones less than 2 mm will pass it in about 8 days, he said. 

Olweny noted that the study was a secondary analysis of data from a randomized controlled trial that evaluated the efficacy of thiazides in preventing the recurrence of calcium stones. “The original study was not specifically designed to look at asymptomatic stone passage rates for small renal stones, and therefore, the observed rates may not reflect the most precise estimates,” he said.

Stritt said his group has not studied the size limit of stones that pass spontaneously without symptoms. “This study could serve to construct recurrence prediction models based on medical history and stone burden on CT imaging. More well-designed research on this topic is urgently needed,” he said. “These results should encourage urologists to counsel patients about the possibility of an active surveillance strategy when smaller kidney stones are present.”

The author and independent commentators have reported no relevant financial relationships.

American Urological Association 2023 Annual Meeting. Presented April 28, 2023. Abstract MP16-20.

Howard Wolinsky is a Chicago-based medical freelancer and a patient diagnosed with low-risk prostate cancer who has been on active surveillance since 2010. He is the editor of the Substack newsletter, TheActiveSurveillor.​​

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