Introduction: Stone analysis is important for directing metabolic stone management of patients at risk for recurrent stones. In addition to results from 24h urine collections, knowledge of stone composition serves as a pathway to diagnosis of underlying disorders. The objective of this study was to assess stone composition over time in patients with at least two composition analyses. Methods: We retrospectively reviewed data for patients within our health system with stone composition analyses from 1997 to 2022. Patients with =2 analyses =12 months apart were identified. Stones were collected through spontaneous passage or procedures (shock wave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy). Patients’ predominant stone compositions were defined as the component =60% and were otherwise considered mixed. Stones that were 100% organic material were excluded from analysis. Univariate analyses (chi-square, T test) were used to compare patients’ stone analyses. Results: We reviewed 4131 stone analyses and identified 338 patients with 2 or more analyses and 76 patients who had three or more analyses. Patients were 41% female and averaged 51±14years (min-max 18-84 years) at the time of their first stone composition. Eighty-nine (26.3%) patients had a change in their predominant stone component from the first to second stone; 26 (34.2%) had a change from the first to third stone. The mean time between the first and second stone analyses was 54 months (range 12-188, median 44 months); time between the second and third stone analyses was 76 months (range 14-258, median 61 months). A small number of patients, 3.2% of all calcium oxalate stone formers, changed from predominantly calcium oxalate in the first stone analysis to calcium phosphate in the second. This was not different (P = 0.84, Fisher’s exact test) than the number whose stones changed from calcium phosphate in the first stone analysis to calcium oxalate in the second (3.8%) (figure). Conclusions: Patients’ stone composition demonstrated variability in repetitive analyses. Repeating stone analyses may be an important component of long term medical stone management for individual patients. SOURCE OF Funding: None
