This test measures the amount of troponin I in the blood. Troponin I is a protein found in the heart muscle fibers. It is used to help a healthcare professional diagnose a heart attack.
If the healthcare professional suspects a heart attack has occurred or is in the process of occurring, he or she may order this test.
In order to measure the amount of troponin I in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a rubber tube called a tourniquet is tied around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
Normally, no preparation is required for this test.
If a heart attack has taken place, the amount of troponin I in the blood will start to rise within the first 4 to 6 hours. The healthcare professional may order serial blood tests to see if the levels rise, indicating heart damage. In some cases the first level may be elevated, indicating an impending or a recent heart attack. The levels of this test "peak" at 24 hours and may last in the blood stream for several days. The test can help diagnose a heart attack early to ensure rapid treatment.
Other conditions or illnesses can cause a rise in the troponin level. Examples are a pulmonary embolus (a blood clot in the lung), pericarditis, or myocarditis.
The normal value for troponin I is less than 0.5 ng/ml.