FGF23 and chronic kidney disease: Most of the CKD dogs with stages 1 and 2 showed serum phosphorus concentrations within the range according to IRIS recommendations [1,12], and the maintenance of phosphorus serum levels could be a consequence of the FGF-23 mechanism [3,4,23], and FGF-23 could be already released when a slight increase in serum phosphorus developed; this trigger could still happen when serum phosphorus concentrations have slight increases but still within the range considered adequate or normal [3,4,23].