Biological Parameters for the Diagnosis of Bone Turnover in Dialysis Patient
Pp. 106-121 (16)
Pablo Urena Torres
The skeleton is an endocrine organ regulating a multitude of metabolic functions, including carbohydrates, lipids, energy, and mineral metabolism. Each bone represents a very active functional unit, constantly remodeled in virtue of two opposed processes, bone formation and bone resorption. The equilibrium between these two processes determines the gain, loss, or balance of total bone mass. Most metabolic bone diseases show altered bone resorption/formation ratio. In Chronic Kidney Disease (CKD), secondary hyperparathyroidism is the most common complication. It is characterized by High Parathormone Levels (PTH) and increased bone resorption, which can enhance serum calcium and phosphate levels and expose to fractures, vascular calcification, arterial stiffness and increased risk of mortality. These alterations have now been redefined as CKD-MBD for Mineral and Bone Disorders (MBD) by the KDIGO (Kidney Disease Improving G lobal Outcomes). KDIGO guidelines highlight that bone biopsy remains the gold standard diagnostic test of CKD-MBD and recommend its use in order to distinguish between high and low bone turnover and to rule out mineralization troubles and trace metal deposition. However, this recommendation is difficult to follow because of its invasive method and the lack of specialized bone histology services in most parts of the world. PTH is well correlated with bone turnover and is usually used as a surrogate of bone biopsy; however, PTH clearly fails to provide information on mineralization state, which may lead to wrong diagnosis and therapeutic choices in a substantial number of patients. For these reasons, non-invasive methods for the assessment of bone turnover in CKD-MBD, such as the assessment of molecules which are either derived from bone structures itself (TRAP5b, CTX, ICP, NTX, PYD, DPD, BSP, Galactosyl hydroxylysine, sclerostin, BSAP, and osteocalcin) or closely related to bone metabolism (PTH, vitamin D, and leptin) have been proposed as specific markers of bone remodeling. This article reviews the use of these biochemical markers in the diagnosis and treatment of CKD-MBD.
Bone turn-over, bone resorption, bone formation
Dialyses, Clinique du Landy, Saint Ouen, France, and Departments of Physiology and Nephrology, Hopital Necker Enfants Malades, Assistance Publique-Hopitaux de Paris, France