Troponin is a protein of the striated muscles used as an indicator for myocardial infarction.
Troponin complex includes 3 proteins – troponin C, troponin I, troponin T. These proteins are essential for the muscle contraction of the skeletal muscles and the heart muscle called myocardium.
Troponin itself has three subunits, TnC, TnI, and TnT.
Every subunit has its own function:
- Troponin C is binding to calcium ions and produces a change in TnI;
- Troponin T is binding to tropomyosin and as the result troponin-tropomyosin complex is formed;
- Troponin I is binding to actin to hold the troponin-tropomyosin complex;
Tests that estimate the level of troponin I and T are used for diagnostics of myocardial infarction. Due to immunological distinctions between troponin I and T of the skeletal muscles and the heart muscle, the cardiac troponin assays are specific for the myocardium.
Normally the level of troponin in the blood is too low to be detected by the blood tests, although the level <0.01 ng/mL is normal. However, the cutoff for the diagnosis of myocardial infarction varies according to the test system that was used and the detected type of troponin – I or T.
Troponin test is the best method to verify the myocardial infarction and determine the size of the necrosis. Higher levels of troponin correlate with the larger damaged area. The test is also performed for prognosis of the outcomes.
Cardiac troponin T and I can be used to monitor drug and toxin-induced cardiomyocyte toxicity.
Troponin T becomes increases 2 to 4 hours after the onset of myocardial necrosis, with a peak at about 24 hours, later the level of troponin decreases up to 14 days. When the level of troponin is lower than 0.2 ng/mL repeat measurements at 3 and 6 hours are performed to distinguish an acute and chronic elevation.
If the levels of troponin appear to be normal during 12 hours after the onset of chest pain the diagnosis of myocardial infarction is unlikely.
Levels of troponin may also be increased in case of:
- Tachycardia (abnormally fast heartbeat) and arrhythmias (tachy-, bradyarrhythmias, heart blocks);
- Cardiopulmonary resuscitation and defibrillation;
- Aortic dissection;
- Arterial hyper- or hypotension;
- Pulmonary hypertension (high blood pressure in lung arteries due to pneumosclerosis, chronic pulmonary diseases);
- Pulmonary embolism (blockage of a lung artery by an embolus – a blood clot, fat, or tumor cells);
- Congestive heart failure;
- Coronary artery disease (unstable angina pectoris);
- Myocarditis (inflammation of the heart muscle);
- Prolonged exercise;
- Traumatic injuries of the heart;
- Generalized seizures;
- Extreme exertion;
- Post–cardiac surgery;
- Infiltrative diseases such as amyloidosis;
- Transplant vasculopathy;
- Cardiomyopathy including Takotsubo cardiomyopathy;
- Kidney disease, renal failure;
- Medications and toxins – doxorubicin, trastuzumab, anthracycline, cyclophosphamide, 5-fluorouracil, cisplatin, and snake venom;
- Carbon monoxide or cyanide poisoning.
Even slightly elevated level of troponin in the blood indicates damage to the heart muscle. High levels of troponin refer to the myocardial infarction.
See also the Troponin test
The risks are very low and appear rarely. These include excessive bleeding from the puncture site, hematoma and infection.