Clinical Significance and Laboratory Diagnostics
Measurement of cardiac troponin levels is recommended for all patients with suspected non-ST-segment elevation acute coronary syndrome (NSTE-ACS). The goal of testing is to confirm or rule out myocardial infarction and assess the risk of adverse outcomes.
- Diagnostic Threshold — Concentration exceeding the 99th percentile of the upper reference limit.
- Time Standards — Laboratory results should be reported within 60 minutes of blood collection. If in-laboratory testing is unavailable, qualitative or semi-quantitative point-of-care tests are used. High-sensitivity point-of-care tests are increasingly being implemented.
- Marker Comparison — Cardiac troponins are more sensitive and specific than the MB fraction of creatine kinase (CK-MB) and myoglobin; myoglobin is no longer recommended for routine clinical use.
- Management with Normal Values — If initial serial troponin levels are normal, but clinical suspicion for ACS remains high, repeat testing should be performed at 3 hours or later, especially when using less sensitive assays.
How to Interpret Troponin Changes
Biomarker concentration rises to diagnostic levels within 1–6 hours following an ischemic episode. Confirming acute myocardial injury requires repeat testing to assess dynamic changes (a rise and/or fall in values).
- Acute Myocardial Infarction (AMI) — Diagnosed when there is evidence of acute myocardial ischemia accompanied by a rise and/or fall in troponin values. If baseline levels were normal, a rise and/or fall above the 99th percentile upper reference limit is required. If levels were stably elevated with a variation of no more than 20%, a further increase of >20% from baseline is diagnostic. Infarction is classified as Type 1 (atherosclerosis and thrombosis) or Type 2 (mismatch between myocardial oxygen supply and demand).
- Acute Myocardial Injury — Diagnosed when there is a dynamic change in troponin levels without clinical evidence of acute myocardial ischemia. Etiologies may be ischemic, non-ischemic, or secondary to extracardiac factors.
- Chronic Myocardial Injury — Diagnosed when troponin levels are stably elevated and remain unchanged over serial measurements. Possible causes include structural heart disease, chronic kidney disease, and others.
Causes of Non-Ischemic Elevation
Acute elevations in cardiac troponin are observed not only in Type 1 myocardial infarction due to atherothrombosis, but also in other pathogenetic variants of infarction and acute non-ischemic myocardial injury.
- Heart Failure — Both acute and chronic. In acute decompensated heart failure, troponin levels are almost always elevated, which complicates the diagnosis of acute myocardial infarction and does not always indicate its presence.
- Cardiovascular Pathologies — Pulmonary embolism, myocarditis, cardiomyopathies, and acute aortic syndromes.
- Extracardiac Factors — Sepsis, stroke, and poisonings.
- Renal Dysfunction — Troponin elevation is frequently linked to non-ischemic injury and indicates a high risk of cardiac complications. Chronic kidney disease can be a cause of chronic myocardial injury.
Role in Hypertrophic Cardiomyopathy
Routine testing for high-sensitivity cardiac troponin is not part of the standard workup for hypertrophic cardiomyopathy (HCM). However, elevated troponin levels are associated with:
- The degree of left ventricular hypertrophy.
- The severity of diastolic dysfunction.
- The severity of functional impairment, including myocardial ischemia and the progression of chronic heart failure.