Association of Erythropoietin Resistance Index with Interleukin-6 among Patients Undergoing Conventional and Extended-Hours Haemodialysis

Background: Extended-hours hemodialysis (HD) has better clinical outcomes than conventional HD. In patients with maintenance HD, high level of the erythropoietin resistance index (ERI) is known as the factor of high mortality. Previous studies have reported that Extended-hours HD is associated with lower ERI levels, but the mechanism is unkouwn. Methods: We performed a cross-sectional study of patients with extended-hours HD or conventional HD between January and March 2020. ERI was calculated by dividing weekly erythropoiesis-stimulating agents (ESAs) use by body weight (BW, kg) and hemoglobin (Hb, g/dL). Blood interleukin-6 (IL-6) levels were measured by ELISA kit (HS600C, R&D). Linear and non-linear associations between ERI, ferritin and IL-6 levels were examined across dialysis modalities. Results: A total of 364 participants (176 with extended-hours HD and 188 with conventional HD) were included in the analysis. The mean age was 66 vs 72 years, percentage of men was 68 vs 62%, and the mean Hb was 11.1 vs 11.2 g/dL. Extended-hours HD was associated with lower weekly ESAs use (FigureA). Multivariable linear regression analysis showed that extended-hours HD was associated with lower weekly ESAs use; -3800 U/week (95% confidence interval (CI); -5300 to -2300). In Figure B, restricted cubic spline (RCS) function indicated that extended-hours HD was associated with lower ERI, especially in hypoferritinic conditions (P for interaction <0.01). In conventional HD group, ERI is increased with elevation of IL-6 levels, on the other hans, in extended-hours HD group, ERI appears to remain unchanged despite increased IL-6 levels (FigureC). Conclusion: The patients with extended-hours HD had lower ERI than those with the conventional HD group, especially in hypoferritinic conditions. In extended-hours HD group, higher IL-6 levels tended not to be associated with higher ERIs, which may contribute to better clinical outcomes in patients on extended-hours HD.