The cardiac troponin test detects damage to the heart muscle. Troponin is a protein that appears in the blood only when the heart muscle is damaged, as in a heart attack. There are other causes of elevated troponin, but a heart attack is the most common. The earlier test could not measure the low amounts of troponin normally in blood. Troponin T highly sensitive (hs-TnT) is an advanced test now in use.
What Is Troponin?
Troponins are proteins needed for the contraction of cardiac muscles and skeletal muscles. Skeletal muscles are the muscles that move our limbs and other parts that we control. Cardiac muscle forms the wall of the heart, and is the part most damaged in a heart attack.
Three types of troponin are known — troponin C, troponin I, and troponin T. All three types are present in cardiac and skeletal muscles. The troponin I and troponin T in cardiac and skeletal muscles are different from each other. The tests we use can measure the cardiac types of these proteins particularly. The troponin C of both cardiac and skeletal muscles is identical. Laboratories don't measure this protein.
The two types of cardiac troponin measured by tests are troponin T (TnT) and troponin I (TnI). Both are good markers of heart injury.
What Is a Cardiac Troponin Test?
This test measures the level of troponin in the blood. When the heart is well, troponin is in the heart muscle cells and does not reach the blood. Only when the heart is damaged does troponin appear in the blood.
If a heart artery is blocked, the muscle cells are damaged because of a lack of oxygen. Troponin appears in the blood. The more the damage to the heart muscle, the higher the level of troponin in the blood.
Cardiac Troponin Test — Why Is it Done?
The test is most often done if your physician suspects you're having a heart attack. If you have chest pain, shortness of breath, and other signs of a heart attack, your physician will ask for a cardiac troponin test. Along with this, they may also ask for an electrocardiogram (ECG or EKG) and other blood tests like myoglobin or CPK isoenzymes.
Most people with a heart attack will have a rise in blood levels of cardiac troponin in 3 hours. Levels remain high for 7 to 14 days.
Angina is a chest pain. It is caused by your heart muscles not getting enough oxygen. If you have had angina for a long time or it gets worse, your physician may ask for a cardiac troponin test.
Creatine kinase is a test that also detects heart attacks. But this test is also positive with muscle injuries anywhere in the body. Cardiac troponins are only positive when the heart muscle is damaged.
Your physician can easily diagnose most heart attacks by the ECG and clinical symptoms. But one type, called NSTEMI (non-ST-elevation myocardial infarction), doesn't show the typical changes on an ECG. A cardiac troponin test tells your physician whether or not you have had a heart attack.
High-Sensitivity Cardiac Troponin (hs-TnT)
The normal levels of troponin in the blood are very low. Usual results are 0 to 0.04 nanograms per milliliter. Such low levels are difficult to measure accurately with standard testing.
The troponin T highly sensitive (hs-Tnt) test was developed for more precise measurement. A genetically re-engineered detection antibody is used. This reduces the interference by heterophilic antibodies. The normal range of cardiac troponin by this test is 0 to 14 nanograms per liter.
The normal range is different for women and men. A value of 10 nanograms per liter is considered the upper limit of normal for women. For men, 15 nanograms per liter is considered the cut-off value. Results above these levels in people with chest symptoms show that a heart attack has happened.
The hs-TnT allows the detection of low levels of cardiac troponin. This is very important if you reach the hospital soon after your symptoms start. This test may give a positive result when a regular test doesn't.
The early diagnosis of myocardial infarction (heart attack) is crucial. If your physician can detect it early and start treatment quickly, the outcome is better. Using the hs-TnT detects 34% more people with myocardial infarction.
The detection rate for heart attack by hs-TnT is nearly 100% at 3 hours. If your test is negative 3 hours after you first had chest pain and breathlessness, you almost certainly have not had a heart attack.
High-Sensitivity Cardiac Troponin (hs-TnT) — Other Uses
Heart attack long-term outcome. People who have raised levels of hs-TnT seven weeks after the heart attack were at higher risk of further heart events.
Heart failure. Only 10% of people with heart failure have a positive cardiac troponin test result. The highly-sensitive TnT test detected 92% of these people.
The hs-TnT can predict outcomes. People with heart failure and the low levels of cardiac troponin had a 7.8% death risk in 2 years. Those with the highest levels had a 35.6% mortality.
Pulmonary embolism. This life-threatening condition is caused by a clot detaching from a vein and traveling to the lung arteries. A hs-TnT test is more likely to detect this condition compared to a standard test.
Pulmonary arterial hypertension. An increase in the blood pressure in the pulmonary arteries, leading to strain on the heart and heart failure. Raised hs-TnT is useful for diagnosing pulmonary arterial hypertension. It can also predict future mortality.
People without symptoms. If you're over 65 and have no symptoms of heart disease, regular hs-TnT testing may be useful. An increase of 50% or more in the result predicts heart failure. Your physician can prescribe treatment to protect you.
Other Causes of Elevated Troponin
Apart from heart damage, some other conditions also cause raised levels of cardiac troponin:
- Fast heartbeat
- High pressure in the lung arteries (pulmonary hypertension)
- Congestive heart failure
- Inflammation of the heart muscle (viral myocarditis)
- Blockage of a lung artery by a blood clot (pulmonary embolism)
- Prolonged exercise (for example, triathlons or marathons)
- Injury to the heart, as in a car crash
- Heart surgery
- Heart muscle disorders like cardiomyopathy
- Chronic kidney disease
The introduction of highly-sensitive cardiac troponin tests has improved the treatment of heart disease and other conditions. Your physician can diagnose a heart attack sooner. Early and effective treatment yields better outcomes. Other diseases like heart failure can also benefit from the cardiac troponin test. When your hs-TnT test values are high, but you don't have symptoms of cardiac ischemia, your physician will also consider disorders other than heart attack.