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Cardiac Troponin
Myocardial Muscle Tissue
Videos: High-Sensitivity TnI & Point-of-Care hsTnI
Troponin, a complex of three contractile regulatory proteins, troponin C, T and I, controls the calcium-mediated interactions between actin and myosin in cardiac and skeletal muscles. Troponin-I and T are specific to cardiac muscles, unlike troponin-C which is associated with both cardiac and skeletal muscles. Hence, troponin-C is not used in the diagnosis of myocardial damage.1
Cardiac troponins are released into circulation in response to myocardial necrosis. As such, cardiac troponins, especially cardiac troponin-I (cTn-I), are the preferred biomarkers for the detection of cardiac injury1, and have long assisted physicians in improving diagnostic strategies for the effective management of patients with chest pain.
Background
- Relatively non-specific markers of myocardial damage, such as creatine kinase (CK), creatine kinase-MB (CK-MB), and myoglobin (MYO), were used in diagnostic laboratories prior to the commercial release of the troponin assays.
- Numerous clinical studies on troponin have indicated its superior cardiac specificity in comparison to CK, CK-MB, or MYO.
- Troponin levels remain elevated in the blood longer than CK-MB or MYO, providing an extended diagnostic window for MI.
Cardiac Markers: Approximate Levels vs. Time of Onset Post MI
Clinical Applications
The clinical utility of troponin-I has expanded over the years due to better understanding of the significance of cTn-I in myocardial damage.
Cardiac Troponin-I (cTn-I) in Acute Coronary Syndrome (ACS)
Cardiac troponin has advanced from its initial application in the diagnosis of acute myocardial infarction (AMI) to include risk stratification of patients with ACS, with respect to the relative risk of mortality and therapy orientation.
- It estimates the probability of a patient having an adverse cardiac event in the next 30-60 days.
- It is applicable to patients diagnosed with unstable angina (UA), non-ST segment elevation MI (NSTEMI), and chest pain.
Cardiac Troponin-I (cTn-I) in Myocardial Infarction (MI)
Elevated levels of cardiac troponin are used to diagnose MI in the presence of myocardial ischemia
The 2007 joint European Society of Cardiology (ESC), American College of Cardiology Foundation (ACC), American Heart Association (AHA), and World Heart Federation (WHF) expert consensus document for the universal definition of myocardial infarction defines an elevated troponin level as:
- A measurement exceeding the 99th percentile of a reference control group of normal, non-diseased individuals2
The consensus document also recommends for the universal definition of myocardial infarction that:
- The imprecision of troponin assays used in diagnosing MI be ≤10% coefficient of variation (CV) at this 99th percentile.2
The National Academy of Clinical Biochemistry (NACB) and International Federation of Clinical Chemistry (IFCC) committee supports the joint recommendations of the ESC/ACC/AHA, with the recognition of one additional point.
- Imprecision of <25% at the 99th percentile does not lead to significant patient misclassification if a series of timed (serial) troponin orders are used.3
Non-MI Causes of Elevated Cardiac Troponin-I Levels
cTn-I levels are also elevated in conditions representing ongoing myocardial damage due to non-ischemic etiologies. Examples include:
- Myocarditis
- Pulmonary embolism (PE)
- Stroke
The elevated levels of cTn-I in all the above conditions possess a high prognostic value in relation to morbidity and mortality, irrespective of the cause.4
Interpretation of Cardiac Troponin-I Levels2,5
Impact on Management
Cardiac troponin-I assays have made a tremendous impact on the management of ACS as they facilitate risk stratification and early diagnosis of ACS, thereby improving patient care and outcome. The key benefits of the troponin-I assays include:
- Identifying patients at high risk, either at short- or long-term follow-up
- Justifying the need for more aggressive treatment
- Identifying patients who would benefit from aggressive thrombolytic treatment since elevated troponins are associated with an active thrombotic process.6
Reliable Answers to Critical Cardiac Questions
Siemens Healthcare Diagnostics is the only company offering multiple solutions for high-sensitivity troponin I* testing that meets the current guidelines for MI diagnosis.
Acute cardiac biomarkers, including cTnI and high-sensitivity cTnI*, are available on the following systems from Siemens Healthcare Diagnostics:
*Defined by the ESC/ACC committee as an imprecision level of ≤10% at the 99th percentile of normal.
References:
1. Babuin L, et al. CMAJ. 2005;173:1191-202
http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16275971
2. Thygesen K, et al. J Am Coll Cardiol. 2007;50:2173-95.
http://content.onlinejacc.org/cgi/content/short/50/22/2173
3. Apple FS, et al. Clin Chem. 2007;53:547-51.
http://www.ncbi.nlm.nih.gov/pubmed/17384000?ordinalpos=2&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_Default ReportPanel.Pubmed_RVDocSum
4. Wu AHB, et al. Clin Chem. 2007;53:2086-96.
http://www.clinchem.org/cgi/content/abstract/53/12/2086
5. Bassand JP, et al. Eur Heart J. 2007;88:1598-660.
http://eurheartj.oxfordjournals.org/cgi/content/full/28/13/1598
6. Morrow DA, et al. Clin Chem. 2007;53:552-74. (CVD brochure)
http://www.clinchem.org/cgi/content/full/53/4/552.
