Supplementary Material for: Age Difference in the Association between Hyponatremia and Infection-Related Mortality in Peritoneal Dialysis Patients

Objectives: This study aimed to examine the association of serum sodium with infection-related mortality and its age difference among continuous ambulatory peritoneal dialysis (CAPD) patients. Methods: A total of 1,656 CAPD patients from January 2006 to December 2013 were included in this study. All patients were followed up until December 2018. Hyponatremia was defined as serum sodium <135 mmol/L. Cox proportional hazards regression model was used to investigate the relationship between baseline serum sodium levels and infection-related mortality. Results: Participants were aged 47.5 ± 15.3 years, 666 (40.2%) patients were female. Glomerulonephritis was the main cause of end-stage renal disease (61.1%). After a median of 46 months of follow-up, 507 patients died. Among the deaths, 252 (49.7%) died from cardiovascular diseases, 105 (20.7%) from infections, and 150 (29.6%) from other causes. The overall infection-related mortality was 14.8 events per 1,000 patients-year, which was higher in patients aged ≥50 years than those younger than 50 years (28.3 vs. 5.3 events per 1,000 patients-year). In the entire cohort, hyponatremia at was not associated with infection-related (hazards ratios [HR] 1.66, 95% CI 0.91–3.02) and all-cause mortality (HR 1.14, 95% CI 0.83–1.57) after adjusting for potential confounders. There was a significant interaction by age of association of serum sodium with infection-related (p = 0.002) and all-cause (p = 0.0002) death. Age-stratified analysis showed that compared with control group, hyponatremia was independently related to increased risks of infection-related death, but not all-cause mortality in patients aged ≥50 years, with HR of 2.32 (95% CI 1.25–4.32) and 1.33 (95% CI 0.95–1.87), respectively. Conclusions: Hyponatremia was associated with increased risk of infection-related mortality in CAPD patients aged ≥50 years.