Variability of serum phosphorus and its association with mortality among hemodialysis patients

Objective: To determine the relationship between the variability of serum phosphorus and mortality among maintenance hemodialysis (MHD) patients. Materials and methods: A total of 502 MHD cases were studied from the Shanghai Renal Registry Network. Serum phosphorus variability was indicated by a coefficient of variation (CV). According to the CV median of serum phosphorus, patients were divided into two groups: a high-variability group (CV ≥ 0.226 mmol/L) and a low-variability group (CV < 0.226 mmol/L). Average phosphorus ≤ 1.78 mmol/L was defined as the standard phosphorus group and serum phosphorus > 1.78 mmol/L was defined as the non-standard phosphorus group. The relationship between serum phosphorus variability and all-cause and cardiovascular disease (CVD) mortality was assessed. Results: In the 502 MHD cases, the average age of patients was 63.9 ± 14.60 years, and dialysis vintage was 82.0 (43.0 - 139.0) months. 118 patients (23.5%) died, succumbing to allcause mortality, while 64 patients (14.3%) died from CVD. The high-variability group had increased all-cause mortality (27.7% vs. 19.3%, p = 0.028). Death from CVD was increased in the high-variability group, but had no statistical significance (15.4% vs. 10.0%, p = 0.082). Cox regression analysis showed that older age, low hemoglobin levels, a higher phosphorus CV, and low serum albumin were independent risk factors for all-cause and CVD mortality. The standard group with low-phosphorus variability had a decreased mortality compared with the nonstandard group with high variability (15.3 vs. 29.2%, p = 0.047 and 6.0 vs. 15.0%, p = 0.033, respectively). The Kaplan-Meier method revealed that patients with low phosphorus variability had a decreased all-cause and CVD mortality (p = 0.023 and p = 0.047, respectively) compared with high phosphorus variability patients. Conclusion: Higher phosphorus CV was independently correlated with all-cause and CVD mortality. Low phosphorus variability with on-target levels resulted in decreased patient mortality. Thus, stable serum phosphorus levels may improve survival in MHD patients.