PTH determination in hemodialyzed patients-A laboratory perspective

Osteocytic Sclerostin Expression as an Indicator of Altered Bone Turnover

Renal osteodystrophy (ROD) is a complex and serious complication of chronic kidney disease (CKD), a major global health problem caused by loss of renal function. Currently, the gold standard to accurately diagnose ROD is based on quantitative histomorphometric analysis of trabecular bone. Although this analysis encompasses the evaluation of osteoblast and osteoclast number/activity, tfigurehe interest in osteocytes remains almost nihil. Nevertheless, this cell type is evidenced to perform a key role in bone turnover, particularly through its production of various bone proteins, such as sclerostin. In this study, we aim to investigate, in the context of ROD, to which extent an association exists between bone turnover and the abundance of osteocytes and osteocytic sclerostin expression in both the trabecular and cortical bone compartments. Additionally, the effect of parathyroid hormone (PTH) on bone sclerostin expression was examined in parathyroidectomized rats. Our results indicate that PTH exerts a direct inhibitory function on sclerostin, which in turn negatively affects bone turnover and mineralization. Moreover, this study emphasizes the functional differences between cortical and trabecular bone, as the number of (sclerostin-positive) osteocytes is dependent on the respective bone compartment. Finally, we evaluated the potential of sclerostin as a marker for CKD and found that the diagnostic performance of circulating sclerostin is limited and that changes in skeletal sclerostin expression occur more rapidly and more pronounced. The inclusion of osteocytic sclerostin expression and cortical bone analysis could be relevant when performing bone histomorphometric analysis for diagnostic purposes and to unravel pathological mechanisms of bone disease.

Efficacy of romosozumab in patients with osteoporosis on maintenance hemodialysis in Japan; an observational study

INTRODUCTION

Romosozumab reportedly increases bone mineral density (BMD) potently but might adversely affect cardiovascular disease (CVD). We evaluated the efficacy of romosozumab in osteoporotic HD patients with a high risk of fracture.

MATERIALS AND METHODS

This was a single-center 1-year study in Japanese HD patients. Among 96 HD romosozumab-treated HD patients with high risk of fracture, 76 HD patients completed 1 year of subcutaneous administration of romosozumab (210 mg/4 weeks) for 1 year. Romosozumab-untreated HD patients (n = 55) were also included. Changes in BMD and serum markers, together with fracture occurrence, and CVD events, were monitored.

RESULTS

During romosozumab treatment of 76 HD patients, BMD time-dependently increased significantly by 15.3% ± 12.9% at the lumbar spine (L1-4), and 7.2% ± 8.3% at the femoral neck at 1 year. Serum BAP and total P1NP increased significantly and serum TRACP-5b decreased at 4 weeks. Fragility fractures occurred in three (3.8%) patients. Hypocalcemia occurred at 4-48 weeks despite the increased dosing of active vitamin-D derivatives, but without any symptom. New CVD events occurred in 5.2% of romosozumab-treated HD patients and10.9% in romosozumab-untreated HD patients.

CONCLUSIONS

BMD was increased significantly during romosozumab treatment at the lumbar spine, and the femoral neck, respectively, at 1 year in HD patients. Hypocalcemia occurred but without any intolerable event. There was no apparent increase in CVD events during 1 year of study, suggesting romosozumab as a promising agent for HD patients with severe osteoporosis.

Diagnostic Accuracy of Noninvasive Bone Turnover Markers in Renal Osteodystrophy

RATIONALE & OBJECTIVE

Bone biopsy remains the gold standard for diagnosing renal osteodystrophy as comparable non-invasive alternatives have yet to be established. The aim of this study was to investigate the diagnostic accuracy of biochemical markers of skeletal remodeling to predict bone turnover.

STUDY DESIGN

Cross-sectional retrospective diagnostic test study.

SETTING & PARTICIPANTS

Patients with chronic kidney disease stages G4-G5D and kidney transplant recipients with successful transiliac bone biopsies.

TESTS COMPARED

Bone turnover as determined by bone histomorphometry was compared to the following biochemical markers: Full-length (1-84) parathyroid hormone (PTH), bone-specific alkaline phosphatase (BsAP), intact procollagen type I N-terminal propeptide (PINP), and tartrate-resistant acid phosphatase isoform 5b (TRAP5b).

OUTCOME

Diagnostic performance was evaluated by area under the receiver operator characteristics curve (AUC), sensitivity, specificity, and negative and positive predictive values. Optimal diagnostic cutoffs were determined in an exploration cohort (n=100) and validated in a separate cohort (n=99).

RESULTS

All biomarkers differed across categories of low 33 (17%), normal 109 (55%), and high 57 (29%) bone turnover. AUC values were in the range of 0.75 - 0.85. High negative predictive values (≥90%) were found for both high and low bone turnover, indicating the ability to rule out both conditions using the suggested biomarker cutoffs. The highest diagnostic performances were seen with combinations of biomarkers, with overall diagnostic accuracies of 90% for high turnover, and 78% for low turnover. Results were comparable for kidney transplant candidates and recipients in a sensitivity analysis.

LIMITATIONS

The single-center approach and heterogeneity of the study cohort are main limitations of this study.

CONCLUSIONS

We conclude that the diagnostic performance of biochemical markers of bone turnover is acceptable, with clinical utility in ruling out both high and low turnover bone disease.