Longer serum phosphorus time in range associated with lower mortality risk among peritoneal dialysis patients: a multicenter retrospective cohort study

Abstract

Background: Relationship between serum phosphorus time in range and mortality risk in peritoneal dialysis (PD) patients remains uncertain. We aimed to evaluate the association between serum phosphorus time in range and all-cause mortality in Chinese PD population.

Methods: This was a multicenter, retrospective, cohort study of 1,915 patients collected from January 2008 to October 2020 in 4 Chinese centers. Serum phosphorus time in range was estimated as the months during the first year that a patient's serum phosphorus level was within the target range (defined as 1.13-1.78 mmol/L). The primary outcome was all-cause mortality. The secondary outcomes were cardiovascular (CV) mortality and PD withdrawal. Cox proportional hazards regression model with comprehensive adjustments was used to assess the association.

Results: The primary outcome occurred in 249 (13.0%) PD patients over a median follow-up of 28 months. Overall, the serum phosphorus time in range was negatively associated with all-cause mortality (per 3-month increments, adjusted HR [aHR], 0.83; 95%CI: 0.75-0.92), CV mortality (per 3-month increments, aHR, 0.87; 95%CI: 0.77-0.99), and PD withdrawal (per 3-month increments, aHR, 0.89; 95%CI: 0.83-0.95). Competing-risk model showed that the relationship of serum phosphorus time in range with all-cause mortality remained stable. None of the variables including demographics, history of diabetes and CV disease, as well as several PD-related and clinical indicators modified this association.

Conclusions: PD patients with longer serum phosphorus time in range in the first year was negatively associated with all-cause mortality and CV mortality. Our findings highlight the importance of maintaining serum phosphorus levels within 1.13-1.78 mmol/L for PD patients.

Keywords: All-cause mortality; Cardiovascular mortality; Peritoneal dialysis; Peritoneal dialysis withdrawal; Serum phosphorus; Time in range.

Fig. 1

Flowchart of patient selection into the study cohort. Abbreviations: CAPD, continuous ambulatory peritoneal dialysis; HD, hemodialysis

Fig. 2

Timeline of phosphorus exposure and follow-up for clinical outcomes. Notes: Baseline values were collected before PD initiation. The exposure of interest was serum phosphorus time in range in the first PD year. Long-term clinical outcomes including all-cause mortality, CV mortality and PD withdrawal were followed up starting from the second year. Abbreviations: PD, peritoneal dialysis; SP, serum phosphorus; CV, cardiovascular

Fig. 3

Association between serum phosphorus time in range in the first PD year and risk of all-cause mortality in various subgroups. Notes: ^a If not stratified, adjusted for age, gender, BMI, smoking, alcohol drinking, diabetes history, CVD history, baseline phosphorus, phosphate-binding and RASi medications, RKF loss (with or without, in the first year), and the mean values of SBP, dialysate GLUC, UF volume, total weekly Kt/V score, LN of iPTH, serum albumin, serum creatinine and blood HGB in the first year after PD initiation. ^b,c,d,e The average values in the first PD year were used. Abbreviations: HR, hazards ratio; CI, confidence interval; BMI, body mass index; CVD, cardiovascular disease; SBP, systolic blood pressure; RKF, residual kidney function; HGB, hemoglobin; ALB, albumin; RASi: renin-angiotensin system inhibitor; GLUC, dialysate glucose concentration; UF, ultrafiltration; LN, natural logarithm; iPTH, intact parathyroid hormone; PD, peritoneal dialysis.