Supplementary Material for: Iron indices mediate but not modify association of parathyroid hormone with erythropoietin resistance in hemodialysis patients

Introduction: Disordered iron balance and abnormal parathyroid hormone (PTH) concentrations, both prevalent in hemodialysis patients, are risk factors of erythropoietin (EPO) resistance. Few studies have evaluated the correlation between iron indices and PTH and the potential role of iron markers on the association of PTH with EPO resistance in hemodialysis population. Methods: In this cross-sectional study of 71 maintenance hemodialysis patients, iron indices including hepcidin, ferritin, reticulocyte hemoglobin content (CHr) and transferrin saturation (TSAT) were examined. EPO responsiveness was measured as EPO resistance index (ERI). Lowess regression curves were performed to explore the cor-relations of iron indices, PTH and ERI. The association between PTH and ERI was modeled using linear regressions. Potential role of iron indices on this association was examined using stratified analyses and mediation analyses. Results: The average ERI value of 10.3 ± 5.3 IU w−1 kg−1 (g/dL) −1. ERI was linked to PTH, hepcidin, CHr and TSAT (all P<0.05). PTH was associated with ERI levels (β=0.007, 95%CI: 0.002-0.012, P=0.007). Hepcidin and PTH were closely correlated with each other (r = 0.28, P = 0.020). No clinically significant interaction between iron indexes and PTH was identified. Hepcidin appeared to mediate about one-fourth of the total association between PTH and ERI in hemodialysis population (25.71%, P=0.020). Conclusion: Iron indices and PTH levels were related to ERI values. Hepcidin ap-peared to be closely correlated to PTH and partly mediate the association between PTH and ERI in he-modialysis population.