The primary diagnostic biomarkers of myocardial necrosis are cardiac troponin I and cardiac troponin T. Features that favor troponins for detection of ACS include high concentrations of troponins in the myo- cardium; virtual absence of troponins in nonmyocardial tissue; high-release ratio into the systemic circulation (amount found in blood relative to amount depleted from myocardium); rapid release into the blood in proportion to the extent of myocardial injury; and the ability to quantify values with reproducible, inexpensive, rapid, and easily applied assays. The 2012 Third Universal Definition of MI provides criteria that classify 5 clini- cal presentations of MI on the basis of pathological, clinical, and prognostic factors.21 In the appropriate clinical context, MI is indicated by a rising and/or falling pattern of troponin with 1 value above the 99th percentile of the upper reference level and evidence for serial increases or decreases in the levels of The potential consequences of emerging high- sensitivity troponin assays include increases in the diagnosis of influenced by the definition of an abnormal tro- The recommendations in this section are formu- lated from studies predicated on both the new European Society of Cardiology/ACC/AHA/World Health Organization criteria21 and previous criteria/ redefinitions of MI based on earlier-gener- ation troponin assays (Appendix 4, Table A). 3.4.3. Cardiac Troponins See Online Data Supplement 4 for additional information on cardiac troponins. Of the 3 troponin subunits, 2 subunits (troponin I and troponinT) are derived from genes specifically expressed in the myocardium. 