Unlike cFGF23, FC did not affect iFGF23 levels in either CKD or non-CKD patients, likely because FC decreased elevated production and cleavage of FGF23 as well as elevated C-terminal cleavage fragments by correcting iron deficiency. This resulted in a decrease in cFGF23 levels without altering the need for iFGF23 levels. Here, FGF23 is linked to chronic kidney disease.