PTH and osteoporosis: The pre-IS levels of some bone metabolism markers (PTH, Ca2+, N-MID, TPINP, and β-CTX) were positively associated with the degree of osteoporosis or fracture risk, and the changes of some bone metabolism markers (Ca2+, Pi, and TPINP) also had associations with osteoporosis and bone status, but these may be age and sex dependent.