FGF23 and chronic kidney disease: In previous studies of CKD patients with eGFR <60 mL/min/1.73 m2, including ours1,19 even though serum PTH and FGF23 were increased, either serum 1,25(OH)2D or 24,25(OH)2D was decreased along with a decline in eGFR, indicating that decreased conversion of 1,25(OH)2D and 24,25(OH)2D from 25(OH)D is the result of a reduction in functional PTECs to metabolize 25(OH)D.