title: Validation of commercially available ELISAs for the detection of circulating sclerostin in hemodialysis patients.
abstract: BACKGROUND
  Sclerostin is an endocrine regulator in chronic kidney disease - mineral and bone disorder (CKD-MBD). Validation of assay comparability and pre-analytical handling is mandatory for establishment of sclerostin as a biomarker.
  
  
  METHODS
  Blood samples (serum, EDTA, heparin and citrate plasma) were obtained from 12 hemodialysis (HD) patients after the long dialysis interval. Passing-Bablok regression analysis and Bland-Altman difference plots were used to evaluate the agreement between sclerostin levels measured with two commercially available ELISAs from TECOmedical and Biomedica.
  
  
  RESULTS
  Independent of the sample type, the agreement of the two assays was poor with a strong proportional but no systematic bias. Compared to the TECOmedical assay, the Biomedica 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 for plasma samples. Among the 3 different plasma samples no systematic error could be documented.
  
  
  CONCLUSIONS
  Careful consideration 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.
authors.affiliation: Department of Cardiology, University Hospital of the RWTH Aachen, Germany.
authors.forename: Sebastian F
authors.initials: SF
authors.lastname: Mause
authors.affiliation: Department of Cardiology, University Hospital of the RWTH Aachen, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Deck
authors.affiliation: TECOmedical AG, Sissach, Switzerland.
authors.forename: Mark
authors.initials: M
authors.lastname: Hennies
authors.affiliation: Department of Nephrology, University Hospital of the RWTH Aachen, Aachen, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Kaesler
authors.affiliation: Department of Medicine, University Hospital Leuven, Leuven, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Evenepoel
authors.affiliation: Center for Cardiovascular Research, John A. Burns School of Medicine, University of Hawaii, Honolulu, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Boisvert
authors.affiliation: Department of Nephrology, Klinikum Maria-Hilf, Mönchengladbach, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Janssen
authors.affiliation: Department of Cardiology, University Hospital of the RWTH Aachen, Germany.
authors.forename: Vincent M
authors.initials: VM
authors.lastname: Brandenburg
keywords: CKD-MBD; biomarker; haemodialysis; sclerostin; vascular calcification