Sensitive Cardiac Troponin Assays: Myth and Magic or a Practical Way Forward?
Cardiac troponins (cTn) are considered to be the ‘gold standard’ biomarkers for the diagnosis of acute coronary syndrome (ACS) a pathological spectrum which includes cardiac ischemia, angina, myocardial infarction and ultimately cardiac failure. The growing evidence base for the diagnostic and prognostic use of cTn in ACS has resulted in a universal redefinition of acute myocardial infarction (AMI). A diagnosis of AMI includes the detection of an elevated cTn (or CK-MB) with at least one measurement within 24 hours of the cardiac episode being >upper 99th percentile of a reference population, in conjunction with evidence of myocardial ischemia. A number of high sensitivity immunoassays with claims of superior imprecision and a definable 99th percentile have been produced. Clinically, these have two important impacts. First, there is a drive to change the values into whole numbers by the application of a unit change which carries the scope for confusion. Secondly, the near-normal Gaussian distribution of sensitive cTn in healthy subjects will increase the frequency of cTn positivity in the non-ACS population. The problem is to decipher if such minor elevations in cTn are of clinical concern. What is certain is that AMI remains a clinical not a biochemical diagnosis and the interpretation of cTn concentrations should be made according to the clinical context.
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