Introduction: High serum phosphorus (P) has been shown to be associated with a more rapid decline of renal function in patients with chronic kidney disease (CKD).
Objective: The aim of this study was to determine whether time-averaged serum P levels are associated with the progression of renal failure adjusted for other potential confounders.
Patients and methods: A prospective observational study of 184 patients with pre-dialysis CKD, stages 3, 4 and 5 (mean GFR=15.2±5.6 ml/min/1.73 m2). The rate of decline in renal function was calculated as the slope of GFR. Median follow-up time was 303 days. Biochemical parameters were analysed as time-averaged concentrations. Multivariate linear regression analysis was used to assess the best determinants of serum P levels, and the relationship between the rate of decline of renal function and the study covariates.
Results: The best determinants of serum P levels were: GFR (beta = 0.477), female sex (beta = 0.106), serum calcium (beta = -0.274), serum albumin (beta = -0.112), serum bicarbonate (beta = -0.182), protein catabolic rate (beta = 0.144), and use of diuretics (beta = 0.180). The mean ± standard deviation (SD) slope of GFR was -0.198±0.376 ml/min/month. The best determinants of the slope of GFR were: proteinuria (beta = -0.462), serum P (beta = -0.440), and basal GFR (beta = -0.404). Total urinary P excretion was not significantly associated with the rate of decline of renal function.
Conclusion: High serum P levels are strongly and independently associated with a more rapid decline of renal function in patients with advanced CKD.