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. Srčani troponini (cTn) smatraju se »zlatnim standardom« među biomarkerima za dijagnostikovanje akutnog koronarnog sindroma (ACS), patološkog spektra koji obuhvata srčanu ishemiju, anginu, infarkt miokarda i konačno prestanak rada srca. Sve veći broj dokaza koji idu u prilog dijagnostičkoj i prognostičkoj upotrebi cTn u ACS doveo je do opšteg ponovnog definisanja akutnog infarkta miokarda (AMI). Dijagnoza AMI uključuje detekciju povišenog cTn (ili CK-MB) - najmanje jednom u 24 časa od srčane epizode izmeren je nivo > gornjeg 99. procenta referentne populacije - uz dokaze o ishemiji miokarda. Izrađeno je nekoliko veoma osetljivih imunoeseja s navodno superiornom nepreciznošću i 99. procentilnom vrednošću koji se može definisati. U kliničkom smislum, oni imaju dvojaku važnost. Prvo, postoji težnja da se vrednosti promene u cele brojeve, menjanjem jedinice koja unosi zabunu. Drugo, gotovo normalna Gaussova raspodela osetljivog cTn kod zdravih subjekata povećaće učestalost pozitivnog cTn u populaciji bez ACS. Problem je kako utvrditi da li su ti blago povišeni nivoi cTn od kliničkog značaja. Ono što je sigur