FGF23 and chronic kidney disease: Log FGF23 was strongly inversely associated with GFR in a non-linear fashion in both CKD (β = −0.79, p < 0.001) and CKD-T (β = −0.70, p = 0.003) patients, with the threshold for high FGF23 (>101 RU/mL) at a GFR of 47 ml/min/1.73 m2 (Fig. 2).