Tom No: Dear members and guests. A recent clinical study among patients with bilateral nephrolithiasis demonstrated that fewer subsequent stone-related events were experienced when patients underwent ureteroscopy on both the symptomatic, as well as the contralateral asymptomatic side as opposed to ureteroscopy only on the symptomatic side. However, the study did not separate patients based on whether or not their stone disease was optimally managed metabolically. Accordingly, we evaluated how optimization of calcium oxalate supersaturation after unilateral ureteroscopy among patients with bilateral stone disease might affect subsequent stone-related events in the unoperated asymptomatic kidney.

We conducted a retrospective chart review comparing 23 patients with calcium oxalate supersaturation greater than 4.5 to 24 patients with calcium oxalate supersaturation less than 4.5. All patients had one to six median five millimeter stones on the non-operated side.

Our primary outcomes were the incidence of symptomatic ureterolithiasis on the untreated side resulting in emergency department visits or surgery. Our secondary outcome was the contralateral stone disease progression measured as linear or volumetric stone growth or new stone formation on two consecutive non-contrast CT scans averaging a year apart.

We define linear stone growth as an increase in size of one millimeter or more, and volumetric stone growth as an increase in 20% or more. Additionally, we evaluated the effects of calcium oxalate supersaturation on yearly stone growth, defined as the cumulative percentage stone growth divided by total months of CT follow-up. There was no significant difference in subsequent surgeries, or emergency department visits. Neither was there a significant difference in stone disease progression between patients with the supersaturation greater than or less than 4.5 for both linear measurements, as well as volumetric determinations.

However, in our linear regression model, there was a statistically significant association between increasing calcium oxalate supersaturation scores and yearly stone growth rate, both for linear measures and volumetric measures. This trend was more evident when volume was a determining metric.

In conclusion, at an average follow-up of three years, optimization of calcium oxalate supersaturation scores was not associated with a significant decrease in subsequent emergency room visits or surgery on the asymptomatic side among patients with bilateral calcium oxalate stone disease. However, yearly stone growth rate was notably less among patients in whom the calcium oxalate supersaturation score was lower.