Patients treated for uric acid stones reoccur more often and within a shorter interval compared to patients treated for calcium stones.

Introduction: We aimed to investigate the association between stone composition and recurrence rate in a well-characterized group of patients.

Methods: From our prospectively assembled database of 1328 patients undergoing ureteroscopy and percutaneous nephrolithotomy (PCNL) between 2010 and 2015, we identified 457 patients who met the inclusion criteria: a minimum of two years' followup, stone-free status following surgery, normal anatomy, and Fourier transform infrared (FT-IR) stone analysis results. Stone recurrence was identified by kidney-ureter-bladder (KUB) or an ultrasound (US). All symptomatic events were recorded. Kaplan-Meier and Cox proportional hazard regression methods were used to assess the differences in recurrence rates and associated risk factors.

Results: Calcium oxalate (CaOx), uric acid (UA), and struvite stones were found in 298 (65.2%), 99 (21.7%), and 28 (6.1%) patients, respectively. During a median followup of 38 months (interquartile range [IQR] 31-48), stone recurred in 111 (24%) patients. One-year stone-free rates (SFRs) stratified by composition were: CaOx 98%, UA 91.9%, calcium phosphate 90%, struvite 88%, and, cystine 83%; the two-year SFRs were 92.6%, 82.7%, 80%, 73%, and 75%, respectively. On multivariate Cox regression analysis, UA composition, the absence of medical preventive therapy, and preoperative stone burden were associated with a shorter time to recurrence. Secondary intervention for recurrent, symptomatic stones was required in 11 (11.1%) and 22 (7.4%) of patients with UA and CaOx stones, respectively (p=0.02).

Conclusions: UA stone-formers are more likely to have a recurrence and to undergo surgical intervention in comparison to CaOx stone-formers, regardless of medical preventive treatment. These differences are more prominent during the first year of followup and should be incorporated into the patient's followup protocol.