alkalization, a cornerstone of cystinuria medical management, may contribute to altered stone composition. The incidence of and predictors for stone conversion among cystinurics are unknown. If such conversion occurs, it may alter management and thus would underscore the need for continued stone analyses. Furthermore, elucidating factors associated with conversion may allow identification of interventions potentially increasing stone proclivity in this cohort of recurrent stone formers.METHODS: We constructed a database of patients with cystinuria from four EDGE institutions. We analyzed medications, stone analyses, 24-hour urinalyses, and prior interventions. We divided the patients into those who only formed cystine stones and those with other stone components and compared these groups to identify risk factors associated with conversion.RESULTS: Among 4 institutions we compiled a database of 104 patients with cystinuria. There were 279 reported stone analyses and 417 stone procedures. Thirty-six (35%) patients submitted stones with non-cystine components and of these, 77% of were calcium phosphate based. 15 (43%) converted more than once. K citrate medication was reported in 63 (66%) of all patients: in 38 (60%) of pure cystine stone patients, and in 24 (75%) of converters (p ¼ 0.1303). For those who converted and took K citrate, the average duration of alkalization therapy was 4.5 years. Regarding surgical management, 13 (12.4%) patients had at least one SWL (range 0 e 10) and 71 (67.6%) had at least one PCNL (range 0-9). When stratified based on pure cystine vs converted stone, the average number of procedures was higher in the conversion group (5.9 vs 3.5, p¼0.0130). When looking specifically at SWL and PCNL there was a higher average SWL amount in the conversion group (0.97 vs 0.07, p¼0.0012) but no difference in PCNL (1.8 vs 1.8, p¼0.9597). On logistic regression, male gender (OR 3.2, p-value 0.0331) and number of SWL (OR 3.05, p-value 0.0229) were associated with increased likelihood of stone conversion.CONCLUSIONS: Conversion to non-cystine stones may occur in over one third of cystinurics. This appears to be more common in men and is associated with prior SWL. Future research with larger cohorts is indicated to further characterize cystine stone conversion and guide best management options.
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