Measurement of troponins is mandatory for all patients with suspected NSTE-MI [1]. High sensitive troponin (hs-cTn) assays (which are able to measure the troponin in at least 50% of a healthy population, with an analytical coefficient of variation (%CV) lower than 10% at the 99th percentile upper reference limit (URL)), have been recently recommended in preference to less sensitive ones [1]. The use of hs-cTn assays have basically reduced the troponin-blind interval due to their ability to detect very small concentrations.

As result, rule-in and rule-out algorithms, based on the absolute hs-cTn value at presentation (above or below the 99th percentile URL) and the changing pattern observed 1-3 hours later, are currently recommended by the European Society of Cardiology (ESC) with a Class I recommendation and are considered safe. To define whether or not a changing pattern is present, one must consider the blood flow and the time between the onset of symptoms and the obtaining of samples. In addition, previous studies gave warning of possible quantitative analytical shifts at these low concentration ranges that may exceed some of the deltas reported in clinical studies and it hasrecently been suggested to consider also the biological variation if hs-cTn assay is available, especially around 99th percentile.

As a consequence, most studies conclude that a 50-60% change, if the initial value is less than 99th percentile, and a 20% change, if the initial value is greater than 99th percentile, are to be considered significant deltas. However, absolute delta (assay dependent), appears superior to relative per cent changes with hs-cTn assay and in some studies this is particularly so when the initial value is increased [11]. The critical point is that due to the fact that each patient should have more than one sample tested in orderto evaluate the hs-cTn changes, in a laboratory equipped with more than one instrument, these samples may randomly be assayed by different instruments. This may lead to possible misclassification, as previously demonstrated by a contemporary assay. The aim of this study is to measure inter-identicalinstrument bias in our laboratory in order to understand if it can compromise the interpretation of absolute delta value for rapid algorithm 0-3 hours.

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Regards
Denise Williams
Managing Editor
Biomarkers Journal