What is Troponin I ?

Also Known As: TnI, TnT, cTnI, cTnT, high-sensitivity troponin, hs-troponin

Formal Name: Cardiac-specific Troponin I and Troponin T

Troponins are a group of proteins found in skeletal and heart (cardiac) muscle fibers that regulate muscular contraction. Troponin tests measure the level of cardiac-specific troponin in the blood to help detect heart injury.

There are three types of troponin proteins: troponin C, troponin T, and troponin I. Troponin C initiates contraction by binding calcium and moves troponin I so that the two proteins that pull the muscle fiber shorter can interact. Troponin T anchors the troponin complex to the muscle fiber structure. There is little or no difference in troponin C between skeletal and cardiac muscle, but the forms of troponin I and troponin T are different. Measuring the amount of cardiac-specific troponin T or troponin I in the blood can help identify individuals who have experienced damage to their hearts.

Normally, troponin is present in very small to undetectable quantities in the blood. When there is damage to heart muscle cells, troponin is released into the blood. The more damage there is, the greater the concentration in the blood. Primarily, troponin tests are used to help determine if an individual has suffered a heart attack. They may also be helpful in evaluating someone for other forms of heart injury.

Many laboratories in the U.S. use high-sensitivity troponin tests since the Food and Drug Administration (FDA) approved them in 2017. Because this version of the test is more sensitive than previous, older versions, it becomes positive sooner and may help detect heart injury and acute coronary syndrome earlier. The hs-troponin test may also be positive in people with stable angina and even in people with no symptoms. When it is elevated in these individuals, it indicates an increased risk of future heart events such as heart attacks.

When a person has a heart attack, levels of cardiac-specific troponins I and T can become elevated in the blood within 3 or 4 hours after injury and may remain elevated for 10 to 14 days.

How is the test used?

High-sensitivity troponin tests are primarily ordered to help diagnose a heart attack and rule out other conditions with similar signs and symptoms. Either a troponin I or troponin T-test can be performed; usually a laboratory will offer one test or the other. The concentrations are different, but they basically provide the same information.

Troponin tests are also sometimes used to evaluate people for heart injury due to causes other than a heart attack or to distinguish signs and symptoms such as chest pain that may be due to other causes. Testing may also be done to evaluate people with angina if their signs and symptoms worsen.

Troponin tests are sometimes ordered along with other cardiac biomarkers, such as CK–MB or myoglobin. However, troponin is the preferred test for a suspected heart attack because it is more specific for heart injury than other tests (which may be elevated in the blood with skeletal muscle injury) and remain elevated for a longer period of time.