CKD and Its Risk Factors among Patients with Cystinuria.

BACKGROUND AND OBJECTIVES: Cystinuria is an autosomal recessive disorder affecting renal cystine reabsorption; it causes 1% and 8% of stones in adults and children, respectively. This study aimed to determine epidemiologic and clinical characteristics as well as comorbidities among cystinuric patients, focusing on CKD and high BP.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This retrospective study was conducted in France, and involved 47 adult and pediatric nephrology and urology centers from April 2010 to January 2012. Data were collected from 442 cystinuric patients.

RESULTS: Median age at onset of symptoms was 16.7 (minimum to maximum, 0.3-72.1) years and median diagnosis delay was 1.3 (0-45.7) years. Urinary alkalinization and cystine-binding thiol were prescribed for 88.8% and 52.2% of patients, respectively, and 81.8% had at least one urological procedure. Five patients (1.1%, n=4 men) had to be treated by dialysis at a median age of 35.0 years (11.8-70.7). Among the 314 patients aged ≥16 years, using the last available plasma creatinine, 22.5% had an eGFR≥90 ml/min per 1.73 m(2) (calculated by the Modification of Diet in Renal Disease equation), whereas 50.6%, 15.6%, 7.6%, 2.9%, and 0.6% had an eGFR of 60-89, 45-59, 30-44, 15-29, and <15, respectively. Among these 314 patients, 28.6% had high BP. In multivariate analysis, CKD was associated with age (odds ratio, 1.05 [95% confidence interval, 1.03 to 1.07]; P<0.001), hypertension (3.30 [1.54 to 7.10]; P=0.002), and severe damage of renal parenchyma defined as a past history of partial or total nephrectomy, a solitary congenital kidney, or at least one kidney with a size <10 cm in patients aged ≥16 years (4.39 [2.00 to 9.62]; P<0.001), whereas hypertension was associated with age (1.06 [1.04 to 1.08]; P<0.001), male sex (2.3 [1.3 to 4.1]; P=0.003), and an eGFR<60 ml/min per 1.73 m(2) (2.7 [1.5 to 5.1]; P=0.001).

CONCLUSIONS: CKD and high BP occur frequently in patients with cystinuria and should be routinely screened.