FGF23 and chronic kidney disease: In addition to the arguments described above, it should, however, be borne in mind that there lacks a good representative parameter and validated measure of FGF23-resistance, in that both TmP/GFR (ratio of the maximum rate of tubular phosphate reabsorption to the glomerular filtration rate) and FePi might not reflect FGF23-resistance optimally, especially in the setting of more advanced CKD.