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Assay Characteristics and Diagnostic Improvement from Contemporary to High-sensitivity Troponin I Immunoassays

      To the Editor:
      In a recent study, Reichlin et al
      • Reichlin T.
      • Twerenbold R.
      • Reiter M.
      • et al.
      Introduction of high-sensitivity troponin assays: impact on myocardial infarction incidence and prognosis.
      concluded that the introduction of a high-sensitivity troponin T immunoassay leads to only a modest increase in the incidence of acute myocardial infarction in the emergency department. To verify whether similar conclusions may be replicated using a latest-generation, high-sensitivity troponin I immunoassay, we planned a clinical investigation comparing the results of the prototype Beckman Coulter (Brea, Calif) HS-AccuTnI with those of the previous “contemporary-sensitive” Beckman Coulter AccuTnI method.
      The study population consisted of a series of consecutive patients admitted to the emergency department of the Academic Hospital of Parma with chest pain over 1 week and for whom a final diagnosis of acute myocardial infarction could be excluded according to the universal definition of myocardial infarction.
      • Thygesen K.
      • Alpert J.S.
      • Jaffe A.S.
      • Simoons M.L.
      • Chaitman B.R.
      • White H.D.
      Writing Group on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial Infarction
      Third universal definition of myocardial infarction.
      Troponin was tested at patient admission with both the Beckman Coulter “contemporary-sensitive” AccuTnI and HS-AccuTnI methods on Access 2 (Beckman Coulter). The analytic sensitivity and 99th percentile reference limit are 11 and 34 ng/L for AccuTnI and 2.5 and 32 ng/L for HS-AccuTnI, respectively.
      The final study population consisted of 71 patients (age range, 49-73 years; 41 male and 30 female). The Passing and Bablok regression between methods was AccuTnI = 0.75 × HS-AccuTnI + 2.2, with excellent Spearman's correlation (r = 0.905; P < .001). The 99th percentile reference limits recalculated on our population of patients with nonischemic chest pain did not differ between the former AccuTnI (31.5 ng/L; 95% confidence interval, 27.7-35.4 ng/L) and the novel HS-AccuTnI (27.7 ng/L; 95% confidence interval, 24.6-30.9 ng/L; P = .149). The number of patients with values above the limits of analytic sensitivity was 22/71 (ie, 31.0%) with AccuTnI and 60/71 (ie, 84.5%; Pearson's chi-square statistic 41.7; P < .001) with HS-AccuTnI (Figure 1). However, it is noteworthy that when literature-based thresholds were used for both methods, the frequency of patients exceeding the diagnostic cutoff was identical (ie, 2/71; 2.8% for both) (Figure 1).
      Figure thumbnail gr1
      Figure 1Percentage of measurable values and values exceeding the 99th percentile reference limit in a population of patients admitted to the emergency department with nonischemic chest pain, using the “old” Beckman Coulter (Brea, Calif) AccuTnI and the “new” latest generation, high-sensitivity Beckman Coulter HS-AccuTnI immunoassays.
      The term “high-sensitivity” is seldom used by the diagnostic industry to characterize immunoassays for marketing purposes, reflecting higher sensitivity than a “contemporary-sensitive” method developed by the same company or greater sensitivity than most other commercial immunoassays.
      • Lippi G.
      • Montagnana M.
      • Aloe R.
      • Cervellin G.
      Highly sensitive troponin immunoassays: navigating between the scylla and charybdis.
      It is thus reasonable that the clinical implications of transition from “contemporary-sensitive” to high-sensitivity methods cannot be generalized but may largely depend on the characteristics of the single assays. The results of our study suggest that the diagnostic improvement from “contemporary-sensitive” AccuTnI to HS-AccuTnI is unlikely to increase the identification of acute myocardial infarction at patients' admission to the emergency department.

      References

        • Reichlin T.
        • Twerenbold R.
        • Reiter M.
        • et al.
        Introduction of high-sensitivity troponin assays: impact on myocardial infarction incidence and prognosis.
        Am J Med. 2012; 125: 1205-1213
        • Thygesen K.
        • Alpert J.S.
        • Jaffe A.S.
        • Simoons M.L.
        • Chaitman B.R.
        • White H.D.
        • Writing Group on behalf of the Joint ESC/ACCF/AHA/WHF Task Force for the Universal Definition of Myocardial Infarction
        Third universal definition of myocardial infarction.
        J Am Coll Cardiol. 2012; 60: 1581-1598
        • Lippi G.
        • Montagnana M.
        • Aloe R.
        • Cervellin G.
        Highly sensitive troponin immunoassays: navigating between the scylla and charybdis.
        Adv Clin Chem. 2012; 58: 1-29

      Linked Article

      • Introduction of High-sensitivity Troponin Assays: Impact on Myocardial Infarction Incidence and Prognosis
        The American Journal of MedicineVol. 125Issue 12
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          The study objective was to compare the incidence and prognosis of acute myocardial infarction when using high-sensitivity cardiac troponin assays instead of a standard cardiac troponin assay for the diagnosis of acute myocardial infarction.
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      • The Reply
        The American Journal of MedicineVol. 126Issue 9
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          We thank Lippi and Cervellin for their interest in our work and for sharing their observation in 71 patients presenting with chest pain from causes other than acute myocardial infarction to the emergency department.1 Their findings are important and interesting. However, the authors provide 2 conclusions that are not supported by their findings. First, we would argue that the question of whether the clinical implications of transition from sensitive to high-sensitivity methods can be generalized requires testing in appropriately powered large diagnostic and prognostic studies.
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