Urinary Calcium Excretion and Risk of Chronic Kidney Disease in the General Population

Introduction: High urinary calcium excretion (UCaE) has been shown to lead to accelerated renal function decline in individuals with renal tubular diseases. It is not known whether this association also exists in the general population. Therefore, we investigated whether high UCaE is associated with risk of developing chronic kidney disease (CKD) in community-dwelling subjects. Methods: Urine samples of 5491 subjects who were free of CKD at baseline and participated in the Prevention of Renal and Vascular End-Stage Disease study (a prospective, observational, general population-based cohort of Dutch men and women aged 28-75 years) were examined for UCaE. UCa concentration was measured in two 24-hour urine samples at baseline (1997-1998) by indirect potentiometry. UCaE was treated as a continuous variable and a categorical variable grouped according to sex-specific quintiles for UCaE. UCaE was compared with de novo development of estimated glomerular filtration rate <60 ml/min per 1.73 m(2) and/or albuminuria >30 mg/24 h. Results: Baseline median UCaE was 4.13 mmol/24 h for men and 3.52 mmol/24 h for women. During a median follow-up of 10.3 years, 899 subjects developed CKD. After multivariable adjustment, every 1 mmol/24 h higher baseline UCaE was associated with a 6% lower risk for incident CKD during follow-up (hazard ratio: 0.94 [0.88-0.99], P = 0.02). The association was shown to be significantly nonlinear, with highest risk of CKD in the lowest quintile for UCaE (hazard ratio: 1.28 [0.97-1.68], P = 0.09). There was no association between UCaE and mortality or cardiovascular health during follow-up, suggesting that this association was not a reflection of poor nutritional intake due to bad health. Discussion: These findings indicate that high UCaE does not increase risk of CKD, but rather that low UCaE may be harmful.