Risk of Chronic Kidney Disease in Brushite Stone Formers Compared With Idiopathic Calcium Oxalate Stone Formers

Abstract

To study brushite stone formers (BSFs) change in renal function and overall risk of progression to chronic kidney disease (CKD) over time. A retrospective review of all patients with urolithiasis on stone analysis was performed from 1995 to 2003. Stones were classified as brushite if they had at least 10% brushite composition on analysis. Patients with a minimum of 6 years of clinical follow-up were included in the study. BSFs were matched 1:3 to idiopathic calcium oxalate stone formers (CaOx SF) over the same time period. Estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease equation. CKD was classified according to the National Kidney Foundation definition, with grade 3 defined as <60 mL/min/1.73 m2. We identified 20 BSFs who met the inclusion criteria and matched to 60 CaOx SFs. Pure brushite stones were identified in 13 (65%) patients and 17 (85%) had >50% brushite composition. The median patient age (48 vs 47 years, P = .82) and baseline eGFR were not different between BSF and CaOx SF (74 vs 69 mL/min/1.73 m2, P = .68). No patients had stage IV or higher CKD in either group. At median follow-up of 13.6 years, both eGFR (78 vs 74 mL/min/1.73 m2, P = .61) and change in eGFR (0.31 vs 3.2 mL/min/1.73 m2, P = .92) were similar between groups despite the BSF having a higher stone recurrence rate (80% vs 42%, P = .003). No brushite patients experienced a change in CKD stage. BSFs were not shown to be at increased clinical risk of CKD compared with CaOx SFs at long-term follow-up despite more frequent stone recurrence.