PTH and hyperphosphatemia: Furthermore, high serum phosphate has been reported to inhibit proximal renal tubule hydroxylase enzyme, complicating and further increasing the risk of hyperphosphatemia in CKD patients [18]. A progressive decline in glomerular filtration rate (GFR) in CKD leads to a reduction in the levels of 1,25(OH)2D. The prolonged CKD-associated hypocalcemia and hyperphosphatemia drive the parathyroid gland to secrete more PTH to normalize the serum calcium and phosphate levels, leading to SHP.