Serum phosphate level at initiation of dialysis is associated with all-cause mortality: a multicenter prospective cohort study

Abstract

Introduction: As glomerular filtration rate (GFR) decreases, serum phosphate level increases. Previous reports indicated that serum phosphate level was associated with mortality in patients on dialysis. However, few reports have examined the association using dialysis initiation as the baseline period.

Methods: This was a multicenter prospective cohort analysis including 1492 patients. Patients were classified into four quartiles based on the serum phosphate level at dialysis initiation, with Q1 being the lowest and Q4 the highest. All-cause mortality after dialysis initiation was compared using the log-rank test. The propensity score represented the probability of being assigned to group Q1 or Q2–4. All-cause mortality was compared in propensity score-matched patients by using the log-rank test for Kaplan–Meier curves. All-cause mortality of Q1 was compared with that for Q2–4 using multivariate Cox proportional hazard regression analysis. All-cause mortality was also determined among stratified groups with or without use of phosphate binders.

Results: Significant differences in cumulative survival rates were observed between the four groups (p < .001). After propensity score-matching, mortality was significantly higher in the Q1 group than the Q2-4 group (p = .046). All-cause mortality was significantly higher in the Q1 group after adjustment for history of CAD (hazard ratio [HR] = 0.76, 95% confidence interval [CI]: 0.58 − 1.00, p = .048). However, there was no significant difference between the two groups after adjustment for estimated GFR.

Conclusion: The serum phosphate level at the time of dialysis initiation was associated with all-cause mortality. However, the serum phosphate level was dependent on the renal function.

Keywords:

• Phosphate
• dialysis initiation
• all-cause mortality
• multicenter cohort study
• phosphate binder

Ethical approval

This study was conducted by following Ethical guidelines for Clinical Research by the Japanese Ministry of Health, Labor, and Welfare (created 30 July 2003; full revision 28 December 2004; full revision 31 July 2008) and the Helsinki Declaration (revised 2013) and was approved by the clinical research ethics committees at each AICOPP group facility (the approval number: 20110823-3). The subjects received oral and written explanations of the purpose of the study and provided their consent in writing. Trial registration is UMIN 7096. Registered 18 January 2012.

Acknowledgements

We acknowledge the support provided by the investigators and members of the AICOPP. The Aichi Kidney Foundation funded this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We are grateful to the Aichi Kidney Foundation for partially funding this study (www.ai-jinzou.or.jp/).