Because FGF23 levels as determined with the C-terminal assay are elevated by iron deficiency [Arrow (14) in Fig. 5] [9], which is often observed with erythropoiesis stimulating agent use, our study may have offered a more appropriate setting in which the association between the bioactive form of FGF23 and clinical outcomes can be explored. Here, FGF23 is linked to Iron deficiency anemia.