title: Comparison of three anti-dsDNA assays: performance and correlation with systemic lupus erythematosus disease activity.
abstract: OBJECTIVE
  To investigate the BioPlex 2200 multiplex immunoassay and Farrzyme ELISA assays as alternatives to the established Farr radioimmunoassay for the correlation of anti-dsDNA antibodies in the assessment of disease activity in systemic lupus erythematosus (SLE).
  
  
  METHODS
  Standard protocols were used to verify analytical performance claims. Anti-dsDNA antibody levels in SLE patient specimens (N=105) were measured and assessed for clinical performance using manufacturer cut-off limits along with the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) score.
  
  
  RESULTS
  Assay precision, measurable range and normal reference interval met the manufacturers' stated claims. Agreement between Farr and BioPlex assays was moderate (positive agreement=62%; negative agreement=85%; kappa=0.48), as was agreement between Farr and Farrzyme assays (positive agreement=56%; negative agreement=91%; kappa=0.51). Mean SLEDAI-2K scores differed significantly between the anti-dsDNA positive and negative groups for BioPlex (p=0.0006), but not Farr (p=0.11) or Farrzyme (p=0.34). ROC curve analysis showed a similar area under the curve (AUC) for all three assays (0.76, 0.74, and 0.73 for Farr, BioPlex, and Farrzyme, respectively) in the discrimination of clinically active disease. Furthermore, increased anti-dsDNA levels from BioPlex showed significant correlation with active renal disease. However, results suggested a lower cut-off for the Farrzyme assay for assessment of global disease activity.
  
  
  CONCLUSIONS
  BioPlex and Farrzyme assays had similar overall agreement with the Farr assay, with BioPlex best reflecting disease activity in SLE patients.
authors.affiliation: Department of Clinical Biochemistry, University Health Network, Toronto, Ontario, Canada.
authors.forename: Allison A
authors.initials: AA
authors.lastname: Venner
authors.forename: Dominique
authors.initials: D
authors.lastname: Ibañez
authors.forename: Dafna D
authors.initials: DD
authors.lastname: Gladman
authors.forename: Murray B
authors.initials: MB
authors.lastname: Urowitz
authors.forename: Anne
authors.initials: A
authors.lastname: MacKinnon
authors.forename: Ivan M
authors.initials: IM
authors.lastname: Blasutig
authors.forename: Paul M
authors.initials: PM
authors.lastname: Yip
mesh_terms: D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood*; D004247:DNA / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards; D005260:Female; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D011863:Radioimmunoassay / Q000592:standards; D012015:Reference Standards; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D004247:DNA