While the association between ERFE and hemoglobin(HGB) response to rHuEPO is well-established in nonanemic conditions,such correlation and ERFE kinetics in anemic states remain unclear.We employed two rat models of anemia, chronic kidney disease (CKD)anemia and chemotherapy-induced anemia (CIA), to determine ERFE kineticsand its correlation with HGB responses after rHuEPO administration.The key factors influencing ERFE kinetics were characterized usinga PK/PD modeling approach and supported by experimentation. Here, CYGB is linked to anemia.