The antibody configurations of cardiac troponin I assays may determine their clinical performance.

BACKGROUND Previous studies have shown superior clinical performance of the cardiac troponin I (cTnI) assay from Beckman-Coulter Diagnostics. This assay had a unique combination of monoclonal antibodies with 2 monoclonal antibodies directed against epitopes near the NH(2) terminus of the heart-specific region of troponin I. The approach has been adopted by the new cTnI assay from Abbott Diagnostics. The aim of our study was to investigate whether this approach affects the clinical performance of cTnI assays. METHODS Cardiac troponin concentrations were measured in a random sample of patients with unstable coronary artery disease included in the GUSTO IV trial (n = 696) by the AccuTnI (Beckman-Coulter Diagnostics), Architect cTnI (Abbott Diagnostics), Immulite 2500 cTnI (Diagnostics Products Corporation), and Elecsys 2010 cTnT (Roche Diagnostics) assays and related to the 1-year mortality. The primary cutoff concentrations were based on the 99th percentile upper reference limits and an imprecision (CV) < or =10%. RESULTS The sensitivities of the AccuTnI and Architect cTnI assays in identifying patients who died within 1 year were equal and were significantly higher (P <0.05) than those of the Immulite 2500 cTnI and the Elecsys cTnT assays. The concordance between the AccuTnI and Architect cTnI assays was 97%, but concordances between the Architect cTnI and the Elecsys cTnT assays were 89%-92% with more at-risk patients (P <0.01 to P <0.001) identified by the Architect cTnI assay. CONCLUSIONS The Architect cTnI assay has clinical performance similar to that of the AccuTnI, probably as a result of the inclusion of a monoclonal antibody against troponin I epitope 41-49 in the assay.