FGF23 and hyperphosphatemia: In turn, hypocalcaemia reduces the physiological restrain by the calcium receptor on PTH secretion and increases serum PTH, which contributes to enhanced phosphate excretion.64 Furthermore, high PTH tends to suppress FGF23 synthesis in the bone and, in concert with FGF23, suppresses 1,25D synthesis.64,65 Overall, the CKD-BMD is characterized by hyperphosphataemia, hypocalcaemia, high FGF23, and PTH, and low 1,25 VD levels.