FGF23 and chronic kidney disease: However, in a post hoc study, Prats et al. [49] have assessed the effect of FCM injection on the serum phosphate and c-terminal FGF23 levels in nondialysis CKD patients and no difference between hypophosphatemic and nonhypophosphatemic patients was found in terms of initial 25(OH)D, ferritin, and hemoglobin levels.