PTH and chronic kidney disease: Therefore, the aim of this research is to (1) explore the association between the increasing stages of CKD and the development of cortical PI; (2) judge the mediation effect of several bone metabolism markers (i.e., PTH, β-CTX, T-P1NP, OC, and 25OHD) and dual-energy X-ray absorptiometry (DXA) lumbar spine bone mineral density (BMD) on this association.