Background: Recent evidence attests that high-sensitive (HS) cardiac troponin I (cTnI) immunoassays have practical and organizational advantages for managing patients presenting to the emergency department (ED) with suspected acute myocardial infarction (AMI). Nevertheless, the clinical advantages of these techniques over the former contemporary-sensitive (CS) methods remain elusive. This study was designed to verify whether a HS cTnI immunoassay may decrease the chance of patient misclassification upon ED admission. Methods: The study population consisted of 57 consecutive patients admitted to the ED of the University Hospital of Parma (Italy) with suspected AMI. Blood samples were collected immediately upon ED presentation and cTnI was measured with both CS (Beckman Coulter AccuTnI+3) and HS (Beckman Coulter hsTnI) immunoassays. The best cut-off for diagnosing AMI was derived from receiver operating characteristic (ROC) curves. The imprecision at the assay-specific cut-offs was calculated for both immunoassays by measuring scalar dilutions of a sample with high cTnI value serially diluted with buffer until reaching a virtually unmeasurable cTnI value. The potential impact on patient misclassification was then estimated as the sum of potential false positive and false negative results, expressed as percentage. Results: A final AMI diagnosis was made in 9/57 (16%) patients. The area under the curve (AUC) was not significantly different between CS or HS immunoassays (0.89 vs. 0.90; P=0.393). The best diagnostic cut-offs were 20 and 18 ng/L for CS cTnI and HS cTnI, respectively. The assay imprecision was 22.0% at 20 ng/L for CS cTnI and 3.4% at 18 ng/L for HS cTnI, which were then associated with 3.2% and 0.5% chance of patient misclassification, respectively. Conclusions: The improved diagnostic accuracy represents an additional aspect in favor of introducing HS immunoassays for accurate triage of patients admitted to the ED with suspected AMI, especially in those displaying non-diagnostic cTnI values at presentation.
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