Renal osteodystrophy occurs early during loss of kidney function. There are 26 million American patients with chronic kidney disease (CKD), and almost all patients with CKD stage 5 have abnormal bone histology. Six hundred and thirty bone biopsies from adult CKD-5 patients on dialysis were evaluated by histomorphometry and analyzed using the turnover (T), mineralization (M), and volume (V) classification. There were racial differences; whites exhibited predominantly low turnover (62%), whereas blacks showed mostly normal or high turnover (68%). A mineralization defect was observed in only 3% of patients. In whites, cancellous bone volume was low, normal, or high in approximately the same number of patients, whereas in blacks, cancellous bone volume was high in two-thirds of the patients. More than 80% of blacks and whites with low cancellous bone volume had thin trabeculae owing to low bone formation. Cortical thickness was low in half the whites, whereas it was normal in three-quarters of blacks. Cortical porosity was high in 50% of whites, whereas three-quarters of blacks had high porosity. In summary, the TMV system gives relevant information. It should be expanded to include the architecture of cancellous and cortical bone. There are racial differences. Low bone volume and low bone turnover are more frequent than heretofore appreciated, whereas mineralization defects nowadays are observed rarely in adults. These findings call for an adjustment of the current therapeutic paradigm that takes into consideration race and risk of low bone volume and turnover. The latter have been shown to be associated with increased vascular calcifications. ß

The PTH-(1-84)/C-PTH fragment ratio predicts bone turnover with acceptable precision for biological measurements. Moreover, a change in serum calcium levels is one of the regulators of the relative amount of circulating PTH-(1-84) and its large C-PTH fragments.

Abnormal bone turnover is common in CKD, but its effects on bone quality remain unclear. We qualitatively screened iliac crest bone specimens from patients on dialysis to identify those patients with low (n=18) or high (n=17) bone turnover. In addition, we obtained control bone specimens from 12 healthy volunteers with normal kidney function. In the patient and control specimens, Fourier transform infrared spectroscopy and nanoindentation quantified the material and mechanical properties of the specimens, and we used bone histomorphometry to assess parameters of bone microstructure and bone formation and resorption. Compared with high or normal turnover, bone with low turnover had microstructural abnormalities such as lower cancellous bone volume and reduced trabecular thickness. Compared with normal or low turnover, bone with high turnover had material and nanomechanical abnormalities such as reduced mineral to matrix ratio and lower stiffness. These data suggest that turnover-related alterations in bone quality may contribute to the diminished mechanical competence of bone in CKD, albeit through different mechanisms. Therapies tailored specifically to low-or high-turnover bone may treat renal osteodystrophy more effectively. Bone turnover abnormalities are well known in patients with chronic kidney disease (CKD). 1 These abnormalities encompass a spectrum from severely suppressed to markedly elevated bone turnover. Abnormal bone turnover occurs in approximately 85% of patients with CKD stage 5 on dialysis (CKD-5D), 2 and within this patient group, there is a greater risk of bone fracture than within the general population. [3][4][5] Although turnover abnormalities are well described, 1 little information is available on whether these abnormalities are associated with changes in bone quality. Bone quality is the contemporary term used to refer to the structural and material parameters that collectively enable bone to bear load and resist fracture or excessive deformation. 6,7 The potential link between bone turnover and bone quality is an important question meriting study because of the relatively high incidence of fractures reported to occur with abnormal turnover. [8][9][10][11][12][13][14] Thus, the specific aim of this study was to advance the understanding of this potential link by quantifying how the microstructural parameters, material composition, and nanomechanical properties vary in bone with low-or high-turnover renal osteodystrophy (ROD) compared with bone with normal turnover from normal volunteers. RESULTSAmong 163 iliac crest bone biopsies sequentially screened from patients with CKD-5D on dialysis, 35

In the early stages of renal failure, hyperparathyroidism develops as a compensatory mechanism to control serum levels of calcium, phosphorus and calcitriol. As kidney disease progresses, this ability to maintain mineral homeostasis is lost, leading to the development of renal osteodystrophy (ROD). Over the past decade, the pattern of ROD seen in patients with chronic kidney disease (CKD) has changed. Previously, the majority of patients had mixed uraemic osteodystrophy or aluminium-related osteomalacia. The decreased use of aluminium-based phosphate binders, coupled with improvements in the management of hyperphosphataemia, led to a reduction in the prevalence of these types of ROD. Since the mid-1990s, there has been an increase in the prevalence of adynamic bone disease as a result of increased suppression of parathyroid hormone through the use of calcium-based phosphate binders and calcitriol therapy. Adynamic bone disease is also associated with several clinical factors, such as older age, use of continuous ambulatory peritoneal dialysis and the presence of diabetes mellitus, as well as the use of calcitriol therapy. Studies of calcium metabolism in patients with CKD have shown that adynamic bone disease is a distinct clinical condition that leads to hypercalcaemia via mechanisms different from that seen in high-turnover bone disease. As high calcium x phosphorus product has been associated with soft tissue and vascular calcifications, and increased mortality, optimizing bone health may be an important way of reducing cardiovascular risk in patients with CKD. To do this, novel, effective, non-calcium, non-aluminium phosphate binders will be necessary.

There is no correlation between iPTH and bone turnover in African Americans with ESRD. A substantial number of African American patients with low bone turnover have very high serum PTH levels. Bone histomorphometric results reveal differences in remodeling dynamics and responses to PTH between African American and Caucasian patients. Further studies utilizing newer PTH measurement assays are needed to better delineate the correlation between PTH and bone turnover in the various racial groups.

Vitamin D is an important hormone for mineral homeostasis and the proper formation and maintenance of bone. In addition, vitamin D has broader functions in the body that expand its traditionally known role in mineral balance. In chronic renal failure, calcitriol deficiency contributes to the development and progression of secondary hyperparathyroidism, bone disorders, and altered mineral metabolism. Recent revelations of the broader role of vitamin D also suggest calcitriol deficiency may contribute to decreased cardiac and immune function in chronic renal failure patients. Research on vitamin D has led to a more complete understanding of the actions of vitamin D at the transcriptional level and with respect to the clinical use of vitamin D and its analogs to control parathyroid hormone overactivity and to replace the other D hormone-dependent actions in patients with renal failure. Limitations of vitamin D and its metabolites include hypercalcemia, hyperphosphatemia and suppression of bone turnover with the risk of adynamic bone disease. Vitamin D analogs may offer greater selectivity and potentially greater safety as compared to calcitriol because of their altered relative potency on calcium and phosphorus metabolism. This review focuses on the current understanding of the biological actions of vitamin D and its analogs and the rationale for treating patients with chronic renal failure.

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Abstract. Kidney transplantation corrects most of the metabolic abnormalities that cause renal osteodystrophy. However, many transplanted patients develop osteoporosis and other bone lesions that are related, at least in part, to their immunosuppressive regimen. The precise histologic patterns of bone disease after transplantation are not well defined. In a study designed to investigate this issue, 57 adult posttransplant patients agreed to undergo bone biopsies and blood drawings. There were 32 men and 25 women, mean age 45 ± 2 yr, who had received a kidney transplantation 5.6 ± 0.8 yr before biopsy. History of bone pain, fractures, and avascular necrosis was found in 22, 12, and 7 patients, respectively. Serum creatinine was 1.68 ± 0.1 mg/dl, 21% of patients were hypercalcemic, 63.2% had elevated parathyroid hormone (PTH) (>65 pg/ml), and 91.2% had normal calcitriol levels. Cancellous bone volume/tissue volume was below normal compared to age- and gender-matched control subjects in 56.1% of patients. Bone turnover (activation frequency) was low in 45.6%, normal in 28.1%, and elevated in 26.3% of patients. Bone formation rate/bone surface was low in 59.7%, normal in 35%, and elevated in 5.3% of the patients. Erosion surface/bone surface was high in 21.1% of patients. Mineralization was prolonged in 87.5% of patients, including 9 patients with osteomalacia and 12 patients with focal osteomalacia. Cumulative and maintenance doses of prednisone and time elapsed since transplantation correlated negatively with bone volume and bone turnover (r= -0.32 to -0.59,P< 0.05 to 0.01), whereas cumulative doses of cyclosporine or azathioprine, age, gender, or serum PTH levels did not. Regression analysis identified prednisone as the main factor responsible for low bone volume and bone turnover (r= 0.54 andr= 0.43,P< 0.01). No factors were found to predict delayed mineralization. The present study shows that low bone volume, low bone turnover, and generalized or focal osteomalacia are frequent histologic features in transplanted patients. The effects of age, gender, PTH, and cyclosporine on bone volume and bone turnover are apparently overridden by the prominent effects of glucocorticoids. The prevalence of mineralization defect in the presence of normal serum levels of calcidiol and calcitriol suggests vitamin D resistance and deserves further study.