title: Novel sensitive cardiac troponin I immunoassay free from troponin I-specific autoantibody interference.
abstract: BACKGROUND
  Cardiac troponins (cTnI and cTnT) are the recommended biomarkers of myocardial infarction. As cTn-specific autoantibodies (cTnAAb) can interfere with the cTn detection by state-of-the-art cTnI assays, our objective was to develop a sensitive cTnI immunoassay free from this analytical interference.
  
  
  METHODS
  The assay used antibody-coated spots containing three capture Mabs/Fabs directed against the N-terminus, midfragment and C-terminus of cTnI and a europium chelate-labeled tracer Mab against the C-terminus. Following a 3-h sample incubation and washing, cTnI was quantified by time-resolved fluorometry.
  
  
  RESULTS
  The limit of detection (LoD) was 2.9 ng/L and the assay was linear up to 50,000 ng/L. The total precision of 10% CV was not reached, but 20% CV was reached at 10 ng/L. Mean cTnI (10-50,000 ng/L) recoveries were 100% and 119% in three cTnAAb-positive and two cTnAAb-negative individuals, respectively, verifying the interference resistance of the antibody design used. On average, Architect hs-cTnI assay gave seven-fold higher cTnI concentrations than the new assay but the correlation between the assays was good (r=0.958). Of apparently healthy individuals (n=159), 18% had measurable cTnI values (>LoD) and 10% were cTnAAb-positive. The proportion of measurable cTnI values, however, was significantly higher in cTnAAb-positive individuals (13/16, median cTnI 8.5 ng/L) than in cTnAAb-negative individuals (15/143, median cTnI <LoD) (p<0.001).
  
  
  CONCLUSIONS
  Although the developed sensitive cTnI assay without cTnAAb interference takes too long for diagnostic purposes, it could serve as an important analytical tool for exploring the impact of cTnAAbs for cTn testing and for unraveling the etiology behind cTn-related autoimmune responses.
authors.forename: Tanja
authors.initials: T
authors.lastname: Savukoski
authors.forename: Jenna
authors.initials: J
authors.lastname: Jacobino
authors.forename: Päivi
authors.initials: P
authors.lastname: Laitinen
authors.forename: Bertil
authors.initials: B
authors.lastname: Lindahl
authors.forename: Per
authors.initials: P
authors.lastname: Venge
authors.forename: Noora
authors.initials: N
authors.lastname: Ristiniemi
authors.forename: Saara
authors.initials: S
authors.lastname: Wittfooth
authors.forename: Kim
authors.initials: K
authors.lastname: Pettersson
mesh_terms: D000918:Antibody Specificity; D000937:Antigen-Antibody Reactions; D001323:Autoantibodies / Q000097:blood* / Q000276:immunology*; D006801:Humans; D007118:Immunoassay; D009203:Myocardial Infarction / Q000175:diagnosis / Q000276:immunology*; D012680:Sensitivity and Specificity; D019210:Troponin I / Q000097:blood* / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D019210:Troponin I