UC Irvine

Abnormalities of mineral metabolism are associated with increased mortality in patients with ESRD, but their effects in predialysis chronic kidney disease (CKD) are less well characterized. In this study, the associations between levels of serum phosphorus, calcium, and calcium-phosphorus product and progression of CKD were examined. Historical data were collected on 985 male US veterans (age 67.4 +/- 10.9; 23.9% black) with CKD stages 1 through 5. Unadjusted and multivariable-adjusted relative risks for progressive CKD (defined as the composite of ESRD or doubling of serum creatinine) were calculated for categories of serum phosphorus, calcium, and calcium-phosphorus product using Cox proportional hazards models. Higher phosphorus was associated with a higher risk for the composite end point (adjusted hazard ratio [HR] [95% confidence interval (CI)] for phosphorus levels 3.3 to 3.8, 3.81 to 4.3, and >4.3 versus <3.3 mg/dl 0.83 [0.54 to 1.27], 1.24 [0.82 to 1.88], and 1.60 [1.06 to 2.41]; P = 0.001 for trend). A 1-mg/dl higher phosphorus level was associated with an adjusted HR (95% CI) of 1.29 (1.12 to 1.48; P < 0.001). Higher calcium-phosphorus product also was associated with higher risk for progressive CKD (adjusted HR [95% CI] for calcium-phosphorus products 30 to 35, 36 to 40, and >40 versus <30 mg2/dl2 0.58 [0.36 to 0.94], 0.87 [0.57 to 1.34], and 1.37 [0.91 to 2.07]; P = 0.002 for trend). A 10-mg2/dl2 higher calcium-phosphorus product was associated with an adjusted HR (95% CI) of 1.29 (1.11 to 1.51; P = 0.001). Lower serum calcium showed a trend toward higher risk for progressive CKD but without statistical significance. Higher serum phosphorus and higher calcium-phosphorus product are associated with progression of CKD.