title: Evaluation of the analytical performance of the advanced method for cardiac troponin I for the AxSYM platform: comparison with the old method and the Access system.
abstract: BACKGROUND
  The determination of cardiac troponins is routinely used for rule in/out, risk stratification, and follow-up of patients with acute coronary artery syndrome. We evaluated the analytical and clinical performance of the advanced immunoassay for troponin I (cTnI) carried out on an AxSYM platform (Abbott Diagnostic Division) and compared these characteristics to those of the previous version of this assay and to cTnI on the Access 2 immunoassay system (Beckman Coulter, Inc.).
  
  
  METHODS
  We assayed plasma samples from healthy subjects (n=66) and cardiac patients (n=132) using AxSYM Plus system assays called the old (OLD AxSYM) and advanced TnI (ADV AxSYM) methods and using an Access system.
  
  
  RESULTS
  An improvement in analytical sensitivity (detection limit) was observed for the advanced cTnI AxSYM compared to the previous method (0.014 vs. 0.31 microg/L), while the cTnI value for the 10% CV (i.e., functional sensitivity) was 0.41 microg/L for the ADV and 1.9 microg/L for the OLD method. The kinetics of cTnI release was similar, as evaluated in 25 patients with typical acute myocardial infarction (AMI). A close linear relationship was found between the two methods on the AxSYM system (OLD cTnI=7.436+6.858 ADV cTnI; R=0.968, n=214) and with the Access system (OLD AxSYM=7.154+7.9 Access, R=0.876, n=158; ADV AxSYM=0.23+1.209 Access, R=0.927, n=160). However, wide bias was found between the OLD and ADV AxSYM methods (mean difference 118.4 microg/L, p<0.0001), while more similar results were found between the ADV AxSYM and Access methods (mean difference 2.6 microg/L, corresponding to a mean percentage difference of 17%, p<0.0001). In 106 patients with symptomatic rheumatoid arthritis with high rheumatoid factor (RF) concentration, the mean cTnI measured by the ADV AxSYM method was 0.009+/-0.031 mug/L (range 0-0.23 microg/L) with a significant correlation (R=0.316, p=0.001) between cTnI and RF values. Furthermore, in 60 of these serum samples the cTnI concentration was also measured using the Access method; significant correlation with the values found by the ADV AxSYM method was observed (R=0.468, p=0.0002).
  
  
  CONCLUSIONS
  The present study indicates that the AxSYM Troponin-I ADV immunoassay shows improved analytical sensitivity compared to the OLD AxSYM method, as well as very similar clinical results to those determined using the Access method.
authors.affiliation: CNR Institute of Clinical Physiology, University of Pisa, Pisa, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Storti
authors.forename: Concetta
authors.initials: C
authors.lastname: Prontera
authors.forename: Maria Serena
authors.initials: MS
authors.lastname: Parri
authors.forename: Annalisa
authors.initials: A
authors.lastname: Iervasi
authors.forename: Simona
authors.initials: S
authors.lastname: Vittorini
authors.forename: Michele
authors.initials: M
authors.lastname: Emdin
authors.forename: Gian Carlo
authors.initials: GC
authors.lastname: Zucchelli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Longombardo
authors.forename: Paola
authors.initials: P
authors.lastname: Migliorini
authors.forename: Aldo
authors.initials: A
authors.lastname: Clerico
mesh_terms: D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis; D003324:Coronary Artery Disease / Q000175:diagnosis*; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000592:standards; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000097:blood; D019210:Troponin I / Q000097:blood*
chemical_list: D019210:Troponin I; D012217:Rheumatoid Factor