Cardiac enzyme and protein tests

When your heart muscle goes without oxygen long enough during a heart attack, muscle cells in the heart are damaged and die. During this process, the heart muscle releases enzymes, some of which are only found in the heart muscle. Elevated levels of these enzymes in the blood indicate a heart attack.

Several different types of cardiac enzymes can be detected by using blood tests. Some of the enzymes can be detected very soon after a heart attack begins, making it possible to diagnose a heart attack within 1 or 2 hours of having symptoms. Others remain in your blood for several days, which makes it possible to diagnose a heart attack several days after it has happened.

One specific type of cardiac protein, called troponin, may be present in your blood even though other blood tests and your EKG do not suggest that you've had a heart attack. The presence of this protein may indicate that you are at risk for having a future heart attack. If you have an episode of angina and your troponin test is high, your doctor may conclude that you have unstable angina and treat you accordingly.

Tests for cardiac enzymes and protein

Name of test	How soon does the test show evidence of a heart attack?	How long after a heart attack are results reliable?	How useful is the test in diagnosing a heart attack?
Troponin (T or I)	4–6 hours after the heart attack begins	10–14 days	Very useful
Creatine kinase MB, fraction (CK-MB)	4–12 hours after the heart attack begins	1–3 days	Very useful
Myoglobin	2–4 hours after the heart attack begins	2–3 days	Somewhat useful