Supplementary Material for: Interleukin-6 to albumin ratio as a superior predictor of mortality in end stage kidney disease patients

Background: In patients with chronic kidney disease (CKD), high interleukin-6 (IL-6) and low albumin circulating concentrations are associated with worse outcomes. We examined the IL-6 to albumin ratio (IAR) as a predictor of risk of death in incident dialysis patients. Methods: In 428 incident dialysis patients (median age 56 years, 62% men, 31% diabetes mellitus, 38% cardiovascular disease (CVD)), plasma IL-6 and albumin were measured at baseline to calculate IAR. We compared the discrimination of IAR with other risk factors for predicting 60 months mortality using receiver operating characteristic curve (ROC) and analysed the association of IAR with mortality using Cox regression analysis. We divided patients into IAR tertiles and analysed: 1) cumulative incidence of mortality and the association of IAR with mortality risk in Fine-Gray analysis taking kidney transplantation as competing risk; and 2) the restricted mean survival time (RMST) to 60 months mortality and differences of RMST (∆RMST) between IAR tertiles to describe quantitative differences of survival time. Results: For all-cause mortality, the area under the ROC curve (AUC) for IAR was 0.700, which was greater than for IL-6 and albumin separately, while for CV mortality, the AUC for IAR (0.658) showed negligible improvement over IL-6 and albumin separately. In Cox regression analysis, IAR was significantly associated with all-cause mortality but not with CV mortality. Both high vs low and middle vs low tertile of IAR associated with higher risk of all-cause mortality, subdistribution hazard ratio of 2.22 (95% CI, 1.40-3.52) and 1.85 (95% CI, 1.16-2.95) respectively after adjusting for age, sex, diabetes mellitus, CVD, smoking and estimated glomerular filtration rate (eGFR). ∆RMST at 60 months showed significantly shorter survival time in middle and high IAR tertiles compared with low IAR tertile for all-cause mortality. Conclusions: Higher IL-6 to albumin ratio was independently associated with significantly higher all-cause mortality risk in incident dialysis patients. These results suggest that IAR may provide useful prognostic information in patients with CKD.