Abstract
The measurement of cardiac troponins, either cardiac troponin I or T, has become the culprit of clinical decision making in patients with suspected acute coronary syndrome (ACS), especially in those with non-ST elevation myocardial infarction (NSTEMI). The leading analytical mainstays of cardiac troponin immunoassays include the limit of blank (LoB), limit of detection (LoD), functional sensitivity, the 99th percentile of a healthy reference population, along with the percentage of “ostensibly healthy” subjects displaying measurable values < 99th percentile. The latest generation of cardiac troponin immunoassays, conventionally defined as “high-sensitive” (HS), is characterized by a LoD over 100-fold lower compared to the first commercialized techniques and a percentage of measurable values consistently > 50% in the general healthy population. The very recent commercialization of methods with further improved analytical sensitivity (i.e., “ultra-sensitive” assays), which allow to measure cardiac troponin values in the vast majority of healthy subjects, is now challenging the diagnostic paradigm based on early rule-out of subjects with cardiac troponin values comprised between the 99th percentile and LoD. New diagnostic strategies, entailing assay-specific cut-offs, must hence be developed and validated in large multicenter studies. The aim of this article is to provide an update on commercially available HS and “ultra”-sensitive techniques for measuring cardiac troponins, along with possible implications of increasingly enhanced analytical sensitivity on diagnostic algorithms for evaluating patients with suspected ACS.
Highlights
Despite many efforts made through the adoption of widespread preventive strategies, both morbidity and mortality for acute coronary syndrome (ACS) remain extremely high
The universally agreed analytical mainstays of cardiac troponins (cTns) testing are summarized in Tables 1 and 2, and substantially include limit of detection (LoD), limit of blank (LoB), functional sensitivity and the 99th percentile of a healthy reference population [6,7,8]
Introduction of these so-called “high-sensitivity” (HS) immunoassays, driven by the recent evidence that patients with values of both cardiac troponin I (cTnI) and cardiac troponin T (cTnT) comprised between the LoD and the 99th percentile (i.e., > LoD and < 99th percentile) or between the functional sensitivity of the immunoassay and the 99th percentile (i.e., > LoQ and < 99th percentile) have a higher risk of unfavorable clinical outcomes compared to those with lower values [10,11,12,13,14,15]. Such an enhanced risk of adverse events apparently lasts for a longer period after evaluation in the emergency rooms, since patients with values comprised between the 99th percentile and LoD have an increased rate of 30day major adverse cardiovascular events (MACE)
Summary
Despite many efforts made through the adoption of widespread preventive strategies, both morbidity and mortality for acute coronary syndrome (ACS) remain extremely high. Unlike many other human diseases, the diagnostic approach for patients with suspected ACS has undergone sizable and revolutionary changes since the release of the first diagnostic criteria by the World Health Organization in the early 1970s [2]. Very recent evidence, combining organization and economic endpoints with diagnostic efficiency, confirms that the measurement of additional biomarkers, such as the creatine kinase isoenzyme MB (CK-MB), impose a considerable financial burden for the health care system, without providing incremental value to patient care [5]. The universally agreed analytical mainstays of cTn testing are summarized in Tables 1 and 2, and substantially include limit of detection (LoD), limit of blank (LoB), functional sensitivity ( known as “Limit of Quantitation”; LoQ) and the 99th percentile of a healthy reference population [6,7,8].
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