Similarly, in advanced CKD patients (stages 4–5), multiple regression analysis showed serum FGF23 levels to correlate significantly and inversely with eGFR (β = −0.574, P = 0.0156) and to correlate positively with Pi levels (β = 0.381, P = 0.0051) as independent contributing factors (R2 = 0.813, P<0.0001), but not with renal α-KL levels (Table 4). Here, FGF23 is linked to chronic kidney disease.