Troponin I (TnI), troponin C (TnC) and troponin T (TnT) are proteins that are categorized under the troponin complex. This protein complex is instrumental in facilitating cardiac muscle contraction, which is why elevated troponin levels could be indicative of myocardial damage or myocardial infarction. Since TnI and TnT are specific to cardiac muscles, checking their levels can provide valuable information that may help in diagnosing disorders associated with the myocardium.
When is a Troponin Test Ordered?
Troponin proteins are released into the bloodstream in event of damage to the cardiac muscle. A troponin test is a useful diagnostic test that may be conducted if a patient is exhibiting or experiencing signs of heart damage. The conditions that could raise the level of these proteins include:
- Heart conditions such as myocarditis, supraventricular tachycardia or coronary artery spasm.
- Pulmonary hypertension, kidney disease or pulmonary embolism.
Out of the three proteins that form the complex, it is just the levels of TnI and TnT that are measured for those who are experiencing pain or heaviness in the chest region. Doctors can assess the extent of damage to the heart muscle by testing the levels of TnI and TnT after a heart attack. This test is definitely a useful tool for determining the extent of heart muscle damage. These are very helpful in the diagnosis of unstable angina or heart attack. The reference range of TnI and TnT are 0-0.4 ng/mL and 0-0.1 ng/mL respectively.
After a heart attack, the levels of certain substances in the blood get elevated. These substances are referred to as cardiac biomarkers. The cardiac biomarkers include troponin, creatine kinase, myoglobin and creatine kinase isoenzyme (CK-MB).
- Elevated levels of troponin can be detected within four hours of the heart muscle injury.
- Whenever doctors suspect the patient to be having a heart attack, this test is carried out several times in the next 15-16 hours.
- For someone who has just had a heart attack, troponin levels are bound to stay high for a couple of weeks. Thus, this test can help the cardiologists zero in on the most suitable treatment option.
- If the levels normalize within 12 hours from the time when one started experiencing chest pain, the chances of one having a heart attack are quite less.
- High levels must be taken as a warning sign for future heart problems. One must make certain lifestyle-related changes and seek medical advice to lower the risk of heart disease.
Function of Troponins
These regulatory proteins play a vital role in the process of cardiac muscle contraction. It is basically the change in the concentration of intracellular calcium that causes the muscles to contract and relax.
- TnC binds to calcium ions to bring about changes in TnI. TnT attaches to a protein called tropomyosin to form the troponin-tropomyocin complex that lies within the grooves of actin filaments.
- It is TnI that attaches to actin in thin filaments in muscle cells and helps in anchoring the actin-tropomyocin complex. Whenever calcium ions flow into the cytoplasm and move towards the actin and myosin filaments, they attach themselves to troponin-tropomyocin molecules. This brings about a change in the shape of troponin which in turn causes tropomyosin to move out from its place.
- Once actin-myosin binding sites become exposed, actin and myosin interact with each other. This causes the muscle to contract. When calcium ions are not present in the cytoplasm, troponin takes its normal shape. Since myosin and actin cannot interact due to the non-availability of the actin-myosin binding sites, the muscle relaxes.