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Background: International guidelines stipulate that primarily cardiac troponin (cTn) assays with a coefficient of variation (CV) ≤ 10% at the 99th percentile cutoff should be used for diagnosing myocardial infarction. Point-ofcare (POC) assays usually do not meet these criteria. Here, we sought to confirm the manufacturer-recommended 99th percentile cutoff and CV of the POC assay AQT90 FLEX cTnI.
Methods: 119 healthy persons without cardiac disorders were examined to determine the 99th percentile cutoff and the corresponding CV. This cutoff was validated in a cohort of 80 patients with unstable angina and 71 patients with non-ST-segment elevation myocardial infarction (NSTEMI), who were admitted to a chest pain unit. cTnI concentrations were measured in serial serum samples obtained from these patients at presentation, 3 and 6 hours after admission.
Results: A cTnI concentration of 20 ng/L was found as the 99th percentile cutoff (CV 6.7%). cTnI was ≥ 20 ng/L in 51 (75%), 59 (87%), and 60 (88%) of the NSTEMI patients 0, 3 and 6 hours after admission, respectively. At admission, sensitivity was 76% and specificity 95%. Three and six hours later, sensitivity and negative predictive values increased to 88% and 98.8%, and to 92% and 97%, respectively.
Conclusions: We confirmed the manufacturer recommended 99th percentile cutoff of 23 ng/L and established a CV of 6.7% at 20 ng/L. These results demonstrated that the POC assay AQT90 FLEX cTnI must be classified as “guideline acceptable”.
DOI: 10.7754/Clin.Lab.2013.130426
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