PTH and alkaline phosphatase measurement: There were, however, significant positive associations between serum PTH and serum OPG (rsp = 0.268, p = 0.005; Table 2; Fig 4A), between serum PTH and AP (rsp = 0.279, p = 0.003), and between serum OPG and AP (rsp = 0.259, p = 0.007) (Table 2).