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Original article
A novel troponin I rule-out value below the upper reference limit for acute myocardial infarction
  1. Susan M I Goorden1,
  2. Rudi A van Engelen2,
  3. Liza S M Wong2,
  4. Tjeerd van der Ploeg3,
  5. Gerard J E Verdel2,
  6. Madelon M Buijs1
  1. 1Atalmedial Diagnostic Centres, Hoofddorp, The Netherlands
  2. 2Department of Cardiology, Spaarne Gasthuis, Haarlem, The Netherlands
  3. 3Research Centre Linnaeus Institute Spaarne Gasthuis, Haarlem, The Netherlands
  1. Correspondence to Dr Madelon M Buijs, Atalmedial Diagnostic Centres, PO Box 231, Hoofddorp 2130 AE, The Netherlands; m.m.buijs{at}atalmedial.nl

Abstract

Objective To determine cut-off values for a recently introduced high sensitive cardiac troponin assay (hs-cTnI) which provide similar sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) for acute myocardial infarction (AMI) as known cut-off values for an hs-cTnT assay.

Methods A prospective observational study was performed. Hs-cTnT (Roche) and hs-cTnI (Abbott) were measured in consecutive patients with symptoms suggestive of AMI. Representative measurements (obtained at least 3 h after chest pain has started) and serial measurements with a time delay between 2.5 h and 4.5 h were used to determine cut-off levels. Two independent clinicians adjudicated the final diagnosis.

Results 1490 patients were included in the study of whom 114 (8%) received a final diagnosis of AMI. Receiver operating characteristics analysis showed no statistically significant differences in the areas under the curve between the two assays. Cut-off values for representative hs-TnI were found to be as follows: rule-out: 10 ng/L (sensitivity: 98.2%; 95% CI 95.7% to 100.0% and NPV: 99.8%; 99.5% to 100.0%); rule-in: 70 ng/L (specificity: 90.8%; 89.3% to 92.4% and PPV: 39.7%; 36.1% to 43.3%). For serial measurements we found a Δ rule-out cut-off value of 20 ng/L (sensitivity: 94.9%; 88.0% to 100.0% and NPV: 98.7%; 96.9% to 100.0%) and Δ rule-in cut-off values of 100 ng/L (specificity: 92.7%; 87.9% to 95.8% and PPV: 57.6%; 39.4% to 74.0%) and 300% (specificity: 93.8%; 90.4% to 97.2% and PPV: 61.3%; 51.1% to 71.5%).

Conclusions Cut-off values for hs-cTnI measurements are determined which allow a similar diagnostic classification as compared with hs-cTnT. Importantly, for a rule-out paradigm this cut-off value is unmistakably lower than the upper reference limit.

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