24-Hour Urine Phosphorus Excretion and Mortality and Cardiovascular Events

Abstract

Higher morning serum phosphorus has been associated with cardiovascular disease (CVD) in patients with or without CKD. In patients with CKD and a phosphorous level >4.6 mg/dl, the Kidney Disease Improving Global Outcomes guidelines recommend dietary phosphorus restriction. However, whether phosphorus restriction influences serum phosphorus concentrations and whether dietary phosphorus is itself associated with CVD or death are uncertain. Among 880 patients with stable CVD and normal kidney function to moderate CKD, 24-hour urine phosphorus excretion (UPE) and serum phosphorus were measured at baseline. Participants were followed for a median of 7.4 years for CVD events and all-cause mortality. Mean ± SD age was 67±11 years, estimated GFR (eGFR) was 71±22 ml/min per 1.73 m(2), and serum phosphorus was 3.7±0.6 mg/dl. Median UPE was 632 (interquartile range, 439, 853) mg/d. In models adjusted for demographic characteristics and eGFR, UPE was weakly and nonsignificantly associated with serum phosphorus (0.03 mg/dl higher phosphorus per 300 mg higher UPE; P=0.07). When adjusted for demographics, eGFR, and CVD risk factors, each 300-mg higher UPE was associated with 17% lower risk of CVD events. The association of UPE with all-cause mortality was not statistically significant (hazard ratio, 0.93; 95% confidence interval, 0.82 to 1.05). Results were similar irrespective of CKD status (P interactions > 0.87). Among outpatients with stable CVD, the magnitude of the association of UPE with morning serum phosphorus is modest. Greater UPE is associated with lower risk for CVD events. The association was similar for all-cause mortality but was not statistically significant.