Renal osteodystrophy: what's in a name? Presentation of a clinically useful new model to interpret bone histologic findings.

Renal osteodystrophy begins early in the course of chronic kidney disease and occurs almost without exception in all patients with Stage 5 disease (CKD-5). Bone biopsies and evaluation of mineralized bone sections after double tetracycline-labeling are currently considered the gold standard for diagnosis and classification of renal osteodystrophy. Nevertheless, bone biopsies are rarely employed. This is, at least in part, related to the paucity of nephrologists trained in performance of the procedure and the fact that reports of the histologic results are not easily translatable to clinical practice. Results are usually given qualitatively, using non-uniform classifications or by histomorphometric evaluations which are esoteric to most nephrologists. We suggest here that histomorphometric evaluation can be reserved for research and special situations. Also, the customarily used qualitative classification should be replaced by a clinically useful nomenclature, provided the interpretation is done by an individual with sufficient experience in bone pathology. We present a new interactive nomenclature for renal osteodystrophy that addresses abnormalities of turnover, abnormalities of bone balance, and abnormalities of mineralization. The new nomenclature, thus, includes disorders of high- and low-turnover with consideration of the interrelation with positive or negative bone balance with or without mineralization defect. In this schema, changes in bone status are described as deviations from a norm, and treatment is geared toward normalizing values rather than creating any absolute change in one direction or another. It is hoped that such a classification will be easily usable, clinically more relevant, and more amenable to individualized treatment guidance.