Role of bone biopsy in renal osteodystrophy.

Renal osteodystrophy (ROD), the abnormal bone histology that occurs in the context of kidney disease, is a disease spectrum and not a uniform progressive bone disease. It is an important component of the broad disturbances of bone and mineral metabolism associated with chronic kidney disease (CKD). There are multiple pathogenetic factors which contribute to the histological abnormalities seen on bone biopsy. The patients with ROD are rarely symp-tomatic in the early stages of CKD. It is also noteworthy that the clinical manifestations are usually preceded by biochemical changes that are insidious and subtle. This makes it difficult for the clinician to suspect the presence of bone and mineral metabolism abnormalities without direct testing. The serum calcium, phosphorus, and alkaline phosphatase levels are usually normal until late in the course of CKD. The main screening test for abnormal bone and mineral metabolism is the measurement of parathyroid hormone which is also somewhat delayed. The clinical signs and symptoms are also challenging to interpret because of their slow and non-specific nature which may include vague, ill-defined, bone aches and pains, and muscle weakness. The gold standard for diagnosis of ROD is bone biopsy with mineralized bone histology after double tetracycline labeling, iron staining and aluminum staining. The currently used histomorphometric descriptions of bone histology are not well integrated clinically and a new nomenclature that is clinically more relevant and useful has been proposed. Additional studies are required to define the spectrum of ROD in the current therapeutic era, and to find clinically useful non-invasive biomarkers to improve the treatment and monitoring of the abnormal bone in the setting of CKD.