Associations between Hb and indices of erythropoiesis and hepcidin pretransfusion and posttransfusion. Associations between Hb, erythropoiesis, iron stores, and hepcidin were evaluated in both the pretransfusion and posttransfusion state. (A) Pretransfusion Hb concentration was associated with indices of erythropoiesis GDF-15 (r = −0.54, P = .0019) and EPO (r = −0.61, P = .0004), but not sTfR (not shown, r = −0.14, P = .4682), and also with hepcidin (r = 0.47, P = .0094). (B) Pretransfusion hepcidin was inversely associated with erythropoiesis: GDF-15 (r = −0.57, P = .0011); EPO (r = −0.48, P = .0101); and sTfR (r = −0.43, P = .0199). (C) Pretransfusion hepcidin was positively associated with iron loading (ferritin, r = 0.56, P = .0015) but not with inflammation (CRP, r = 0.01, P = .9627). (D) Posttransfusion Hb was associated with erythropoiesis (GDF-15 [r = −0.58, P = .0018), EPO [r = −0.58, P = .0026]) and hepcidin (r = 0.60, P = .0011), but not sTfR (not shown, r = −0.29, P = .1563). (E) Posttransfusion hepcidin was inversely associated with erythropoiesis: GDF-15 (r = −0.65, P = .0004); EPO (r = −0.71, P = .0001); and sTfR (r = −0.50, P = .0101). (F) Posttransfusion hepcidin was positively associated with iron loading (ferritin, r = 0.44, P = .0258) but not with inflammation (CRP, r = 0.17, P = .4045).