Featured, Nephrology

Removal of asymptomatic kidney stones found to significantly decrease risk of relapse

When compared to patients who had small, asymptomatic kidney stones removed while undergoing surgery to remove larger kidney stones, patients who did not have the smaller kidney stones removed had a significantly increased risk of relapse.

Hard mineral deposits that develop in the kidneys are known as kidney stones. One in ten people are expected to experience kidney stones at some point in their lives. A kidney stone the size of a grain of sand might travel through your body undetected, but a stone greater than 5 mm, or the size of a pea, is likely to require medical intervention since it could cause blockages in the urinary tract. For this reason, larger kidney stones are often surgically removed, while smaller secondary stones are frequently left behind.

In a recently published multicenter randomized controlled trial, a University of Washington research team found that not removing small secondary kidney stones during surgical interventions resulted in a significantly increased risk of relapse. The study classified secondary kidney stones as stones that were asymptomatic and ≤6 mm in size.

Dr. Mathew Sorensen, a professor of urology at University of Washington School of Medicine and co-author of the new study told UW Newsroom, “Before this study, the clinical views were pretty mixed on whether some of these stones should be treated,” he said. “Most clinicians would decide, based on the size of the stone, whether it hit the bar for treatment, and if it did not, you would often ignore the little stones.”

Out of a sample of 73 patients, the group that had the secondary kidney stones removed via ureteroscopy had a longer time to relapse when compared to the control group, who did not have their secondary stones removed (p <0.001). A relapse was defined as an ED visit due to a stone occurring on the same side as the original secondary stone(s) or an intervention required due to the original secondary stone(s).

The treatment group had 16% (6/38) of participants relapse, while the control group had 63% (22/35), demonstrating a significantly reduced risk of relapse among participants in the treatment group. The average duration of surgery for the treatment group was 93.6 minutes, while the average duration of surgery for the control group was 59.8 minutes. The results suggest a relapse rate that is 82% lower among patients who have secondary stones removed along with primary stones. 

The authors state, “After a mean follow-up of 4.2 years, the treatment group had a longer time to relapse than the control group (P<0.001 by log-rank test). The restricted mean (±SE) time to relapse was 75% longer in the treatment group than in the control group (1631.6±72.8 days vs. 934.2±121.8 days).” Additional removal of the small kidney stones led to a median increase in surgery time of 25.6 minutes.

Sorensen explained the relevance of the study’s results by concluding, “I think we have proven through this rigorous study that removal of the small asymptomatic stones is beneficial when feasible and in patients that are candidates to have all their stones treated in one procedure. Leaving the stones behind risks trouble in the future.”

Limitations of this study were that it included a relatively small sample size and had limited representation of racial minority populations. Due to these limitations, further research is needed.


The study was published in New England Journal of Medicine on August 11th, 2022.

Abstract. Background. The benefits of removing small (≤6 mm), asymptomatic kidney stones endoscopically is unknown. Current guidelines leave such decisions to the urologist and the patient. A prospective study involving older, nonendoscopic technology and some retrospective studies favor observation. However, published data indicate that about half of small renal stones left in place at the time that larger stones were removed caused other symptomatic events within 5 years after surgery. Methods. We conducted a multicenter, randomized, controlled trial in which, during the endoscopic removal of ureteral or contralateral kidney stones, remaining small, asymptomatic stones were removed in 38 patients (treatment group) and were not removed in 35 patients (control group). The primary outcome was relapse as measured by future emergency department visits, surgeries, or growth of secondary stones. Results. After a mean follow-up of 4.2 years, the treatment group had a longer time to relapse than the control group (P<0.001 by log-rank test). The restricted mean (±SE) time to relapse was 75% longer in the treatment group than in the control group (1631.6±72.8 days vs. 934.2±121.8 days). The risk of relapse was 82% lower in the treatment group than the control group (hazard ratio, 0.18; 95% confidence interval, 0.07 to 0.44), with 16% of patients in the treatment group having a relapse as compared with 63% of those in the control group. Treatment added a median of 25.6 minutes (interquartile range, 18.5 to 35.2) to the surgery time. Five patients in the treatment group and four in the control group had emergency department visits within 2 weeks after surgery. Eight patients in the treatment group and 10 in the control group reported passing kidney stones. Conclusion. The removal of small, asymptomatic kidney stones during surgery to remove ureteral or contralateral kidney stones resulted in a lower incidence of relapse than nonremoval and in a similar number of emergency department visits related to the surgery. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and the Veterans Affairs Puget Sound Health Care System; ClinicalTrials.gov number, NCT02210650.)

Sorensen MD, Harper JD, Borofsky MS, Hameed TA, Smoot KJ, Burke BH, Levchak BJ, Williams JC Jr, Bailey MR, Liu Z, Lingeman JE. Removal of Small, Asymptomatic Kidney Stones and Incidence of Relapse. N Engl J Med. 2022 Aug 11;387(6):506-513. doi: 10.1056/NEJMoa2204253. PMID: 35947709.

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