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 |