Of the 3 troponin subunits, 2 subunits (troponin I and troponinT) are derived from genes specifically expressed in the myocardium. Cardiac troponin measurements provide highly sensitive results specific for detecting cardiomyocyte necrosis.34,173 Highly sensitive assays can identify cardiac troponin not only in the blood of patients with acute cardiac injury, but also in the blood of most healthy peo- As assay sensitivity increases, a greater proportion of patients will have detectable long-term elevations in troponin, thus requiring consideration of serial changes for the diagnosis of MI.Cliniciansshouldbeawareofthesensitivityofthetestsusedfor troponin evaluation in their hospitals and cutpoint concentrations for clinical decisions. Markedly elevated values are usually related to MI, myocarditis, rare analytical factors, or chronic elevations in patients with renal failure and in some patients with HF. CPGs endorse the 99th percentile of the upper reference level as the appropriate cutpoint for considering myocardial For the diagnosis of acute myocardial necrosis, it is important to determine not only the peak troponin value, but also serial changes: 1. A troponin value above the 99th percentile of the upper reference level is required. Additionally, evidence for a serial increase or decrease 20% is required if the initial value is elevated.21,178 2. For any troponin values below or close to the 99th percentile, evidence for acute myocardial necrosis is indicated by a change of 3 standard deviations of the variation around the initial value as determined by the 3. Clinical laboratory reports should indicate whether sig- nificant changes in cardiac troponin values for the par- ticular assay have occurred. 