Most Sensitive Cardiac Marker for Myocardial Infarction

Introduction to Cardiac Markers

Cardiac troponins (troponin T and troponin I) are the most sensitive cardiac markers for myocardial infarction, significantly superior to CK-MB in detecting myocardial necrosis, as recommended by the American College of Cardiology 1, 2

Cardiac troponins are not normally detected in the blood of healthy individuals, allowing cutoff values to be set just above the assay noise level, which permits detection of even minor degrees of myocardial necrosis with increased sensitivity, according to the American College of Cardiology 1, 2
CK-MB is found in skeletal muscle and blood of healthy subjects, requiring cutoff values to be set several units above the normal range, inherently limiting sensitivity, as noted by the American College of Cardiology 1, 2
Troponins are cardiac-specific proteins with amino acid sequences sufficiently different from skeletal muscle isoforms that monoclonal antibody assays can detect them with high specificity, as stated by the American College of Cardiology 1, 2

Troponin T and troponin I have been demonstrated to be more sensitive and specific markers of acute myocardial infarction than CK-MB in multiple studies, as reported by the European Society of Cardiology 3, 4
Approximately 30% of patients presenting without ST-segment elevation who would be diagnosed with unstable angina using CK-MB are actually experiencing non-Q-wave MI when assessed with cardiac troponin assays, according to the American College of Cardiology 1
In one study of 773 patients without ST-segment elevations, 94% had positive troponin T and 100% had positive troponin I within 6 hours after chest pain onset, as found by the European Society of Cardiology 3, 4

Within the first 6 hours after MI, CK-MB subforms may be both more sensitive and specific than standard troponin assays, though this advantage has been largely eliminated with high-sensitivity troponin assays, as noted by the European Society of Cardiology 3, 4
Myoglobin is a better marker from 3-6 hours after symptom onset compared to CK-MB mass and troponin T, but its maximal negative predictive value reaches only 89% and it lacks cardiac specificity, as reported by the European Society of Cardiology 3, 4
From 7 hours after symptom onset, CK-MB and troponin T have higher negative predictive value than myoglobin, according to the European Society of Cardiology 3, 4

High-sensitivity cardiac troponin assays are recommended over less sensitive ones, as they allow detection of cardiac troponin in 50-90% of healthy individuals at baseline, enabling detection of smaller elevations, as recommended by the European Society of Cardiology 5
Measurement of high-sensitivity cardiac troponin is mandatory in all patients with suspected NSTE-ACS, as it complements clinical assessment and ECG, according to the European Society of Cardiology 5
Troponin levels usually rise within 1 hour when using high-sensitivity assays and remain elevated for several days, as noted by the European Society of Cardiology 5

Elevated troponin levels, even when CK-MB is normal, identify patients at increased risk of adverse outcomes, as reported by the American College of Cardiology 1
Troponin T may be superior to CK-MB mass when assessing prognosis in patients with acute chest pain, according to the European Society of Cardiology 3, 4

Troponins are not 100% specific for ischemic MI, as nonischemic causes of troponin elevation exist in many settings including renal dysfunction, myocarditis, pulmonary embolism, and cardiac procedures, as noted by the European Society of Cardiology and the American Heart Association 5, 6
A dynamic elevation of cardiac troponin above the 99th percentile of healthy individuals indicates MI when clinical presentation is compatible with myocardial ischemia, as defined by the European Society of Cardiology 5
Serial sampling is recommended, as troponin elevations from two successive blood samples improve diagnostic accuracy, according to the American College of Emergency Physicians 7