ARNT and Iron deficiency anemia: Abnormalities in FGF‐23 metabolism mediate hypophosphatemia associated with repeated iron infusions.(3, 5, 41, 42) Experimental data suggest that iron deficiency increases FGF‐23 expression through action on hypoxia‐inducible factors (HIFs), HIF1a and HIF1b.(43, 44) The increase in the production of intact FGF‐23 (iFGF‐23) is usually followed by an increase in the cleavage and generation of c‐FGF23 and N‐terminal fragments and has no impact on phosphate levels.