BACKGROUND Sclerostin is an endocrine regulator in chronic kidney disease –

BACKGROUND Sclerostin is an endocrine regulator in chronic kidney disease – mineral and bone disorder (CKD-MBD). test yielded almost 2-fold higher sclerostin values throughout all sample types. Spike recovery and linear dilution studies revealed a higher accuracy of the TECOmedical assay (97% and 96%) compared to the Biomedica assay (118% and 78%). Sclerostin levels were stable within 4 hours after sample collection in particular when analyzed in plasma. In contrast to the Biomedica assay the TECOmedical showed a systematic but no proportional bias between serum and plasma samples with higher values Cisplatin for plasma samples. Among the 3 different plasma samples no systematic error could be documented. CONCLUSION Careful consideration Cisplatin of the pre-analytical handling and comparative assay validation are necessary to facilitate a more differentiated interpretation of studies reporting circulating sclerostin levels. The presence of a proportional bias demonstrates that in HD patients the two ELISAs for measuring sclerostin should not be used interchangeably. Furthermore caution is necessary when comparing sclerostin results obtained from different blood sample types. Keywords: biomarker CKD-MBD haemodialysis sclerostin vascular calcification INTRODUCTION The close relationship between bone disease mineral disturbances and cardiovascular disorders in patients with chronic kidney disease (CKD) is increasingly acknowledged and has led to the introduction of the term chronic kidney disease – mineral and bone disorder (CKD-MBD)1. One of the recently identified regulators involved in CKD-MBD is the glycoprotein sclerostin a soluble Wnt inhibitor produced mainly in osteocytes. Sclerostin inhibits differentiation and function of osteoblasts and possibly interferes with biological signaling that operates in the vessel wall2. Sclerostin represents a promising biomarker in CKD-MBD since the physiology of sclerostin is altered during renal insufficiency and since the modulation of the Wnt signaling pathway via sclerostin is involved in the development of renal osteodystrophy and in cardiovascular diseases associated with CKD3 4 Moreover measurement of circulating sclerostin in patients with end-stage-renal Rabbit Polyclonal to PDE4C. disease (ESRD) revealed associations with bone mineral density5 cardiovascular mortality in prospective observational cohort studies6 7 and with vascular calcification8–10. Of note some of these studies have reported contradictory results thus awaiting further confirmation. In terms of establishing novel biomarkers assay validation and standardization are essential11. Significant disagreement between different assays measuring the same parameter may impair the comparability of results in a clinically meaningful manner. Indeed a relevant variability among different intact parathyroid hormone assays in patients with ESRD Cisplatin has been confirmed12. Previous studies designed to compare two commercially available sclerostin ELISAs namely the Biomedica and the TECOmedical ELISA identified in various clinical settings a relevant variation of measured sclerostin values therefore limiting the clinical interpretation of reported values and compromising the comparability of studies using different immunoassays for sclerostin detection13–16. Several additional factors such as pre-analytical handling including the choice Cisplatin of blood sample type storage time and matrix interference may affect the quantification of biomarkers. For the robust introduction of sclerostin as a biomarker in CKD-MBD it is thus mandatory to further validate the applied assays and to assess the relevance of pre-analytical variables particularly in (haemodialysis) HD patients. MATERIALS AND METHODS Sample collection Human blood samples were obtained with the written informed consent of the patients and the permission from local ethical committees (RWTH Aachen EC vote number EK 300/11). Blood was drawn by venipuncture after an overnight fast at the end of the long dialysis interval from 12 clinically stable patients with ESRD before undergoing routine hemodialysis. We collected serum and three types of plasma (EDTA lithium heparin and citrate plasma) in standard monovettes (Sarstedt Nümbrecht Germany). Patients (5 men 7 women) were aged 66.6 ± 9.1 years and were on dialysis for a median time of 54 months. For further details regarding the patient population please refer to Supplemental Table 1. Samples were centrifuged after 20 60 120 and 240 minutes at.