Additional file 1: Supplementary Figure S1. Correlation between ERFE and Rec. When all measurements were included, Ln (ERFE) and Ln (Ret) showed a significant positive correlation with r = 0.765 (p < 0.0001). Abbreviations: ERFE erythroferrone, Ret reticulocyte. Supplementary Figure S2. Correlation between ERFE and HEPC. When all measurements were included, Ln (ERFE) and Ln (HEPC) showed a significant negative correlation with r = − 0.866 (p < 0.0001). Abbreviations: ERFE erythroferrone, HEPC hepcidin-25.