The impact of cystinuria on renal function

Purpose: Patients with cystinuria frequently have recurrent renal calculi and may subsequently require multiple stone removing procedures during their lifetime which could have an impact on overall renal function. We determined the potential impact of cystinuria and cystine stone formation on the level of renal function compared to calcium oxalate stone formers. Materials and Methods: Clinical data on 40 cystinuric patients followed at 2 medical centers and 45 such individuals in a large stone population data base were analyzed. These results were compared to data on 3,964 calcium oxalate stone formers enrolled in this data base. Results: Mean serum creatinine plus or minus standard deviation for stone forming cystinuric patients was significantly higher than that of the calcium oxalate cohort (1.13 +/- 0.28 versus 1.01 +/- 0.28 mg./100 ml., p = 0.0001). A significantly greater percentage of cystinuric patients (5.8%) had an abnormally increased serum creatinine compared to the calcium oxalate stone formers (2.2%, p = 0.046). Male gender, increasing number of open surgical stone removing procedures and nephrectomy were significant variables associated with an increased serum creatinine (p = 0.0010, p = 0.0038, p = 0.0133, respectively). An increasing number of open surgical stone removing procedures had a significant positive correlation with performance of nephrectomy in the cystinuric population (p = 0.0166). A significantly greater percentage of cystinuric patients compared to the calcium oxalate cohort were subjected to nephrectomy (14.1% versus 2.9%, p = 0.007). Conclusions: Cystinuric patients have higher serum creatinine levels than calcium oxalate stone formers and they are at more risk for renal loss. When stone removal is required, a minimally invasive approach is preferred.