Troponin T and troponin I (cardiac enzymes)

Cardiac biomarkers (treponins) are endogenous substances released into the bloodstream when the heart muscle is damaged or stressed. Measurement of these biomarkers is used to help diagnose, risk-stratify, and guide treatment for acute coronary syndrome. (1) Cardiac troponins are now the gold standard biomarkers for diagnosing acute myocardial infarction. In contrast to creatine kinase, whose levels usually increase 6 to 12 hours after emergency department presentation, troponin levels are elevated in most cases of acute myocardial infarction within 2 to 3 hours of arrival. (2)

Cardiac Troponins (3,4,5)

• Troponins are protein components of striated muscle. There are three different troponins: troponin C, troponin T and troponin I. Troponins T and I are only found in cardiac muscle
• Troponin I and T are markers of cardiomyocyte injury. They become detectable in serum three to six hours after infarction, peak at 12-24 hours, and remain raised for up to 14 days. There are also high sensitivity assays now available.
• High-sensitivity cardiac troponin (hs-cTn) measurement is recommended in all patients with suspected ACS. If the clinical presentation is compatible with myocardial ischaemia, then a rise and/or fall above the 99th percentile of healthy individuals points to a diagnosis of MI.
• In patients with MI, levels of cardiac troponin rise rapidly (i.e. usually within 1 h if using high-sensitivity assays) after symptom onset and remain elevated for a variable period of time (usually several days). Blood tests are taken at presentation and after 1 hour, or possibly at 2 hours depending on history and results. They can be used to rule in or rule out people who are likely to have had a coronary event.

Note - the modern definition of myocardial infarction, endorsed by the European Society of Cardiology and the American College of Cardiology in the Fourth Universal Definition of Myocardial Infarction (2018), requires a rise and fall in cardiac troponin values with at least 1 value above the 99th percentile upper reference limit, accompanied by clinical evidence of myocardial ischemia, including symptoms, electrocardiographic changes, imaging evidence, or identification of coronary thrombus. (6)

Reference:

1. Jacob R, Khan M. Cardiac Biomarkers: What Is and What Can Be. Indian J Cardiovasc Dis Women WINCARS. 2018 Dec;3(4):240-244.
2. Singh V, Martinezclark P, Pascual M, Shaw ES, O'Neill WW. Cardiac biomarkers - the old and the new: a review. Coron Artery Dis. 2010 Jun;21(4):244-56.
3. NICE. Acute coronary syndromes. NICE guideline NG185. Published November 2020
4. NICE. High-sensitivity troponin tests for the early rule out of NSTEMI. HealthTech guidance HTG552. Published August 2020
5. Chauin A. The Main Causes and Mechanisms of Increase in Cardiac Troponin Concentrations Other Than Acute Myocardial Infarction (Part 1): Physical Exertion, Inflammatory Heart Disease, Pulmonary Embolism, Renal Failure, Sepsis. Vasc Health Risk Manag. 2021;17:601-617.
6. Domienik-Karłowicz J et al. Fourth universal definition of myocardial infarction. Selected messages from the European Society of Cardiology document and lessons learned from the new guidelines on ST-segment elevation myocardial infarction and non-ST-segment elevation-acute coronary syndrome. Cardiol J. 2021;28(2):195-201