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Heart Attack Tests


What is CK and CKMB?

Creatine kinase (CK) is an enzyme—a protein that helps cells perform their normal functions—found in the heart, brain, muscle and blood of healthy people. Blood levels of CK rise when your muscle or heart cells are injured. CKMB is a form of the enzyme that is found mainly in heart muscle. While a high level of total CK can indicate damage to muscle, a high CKMB level suggests that there is disease or damage to the heart muscle specifically.

CKMB levels begin to rise within the first 4 to 6 hours after heart attack symptoms begin and reach their highest level after about 18 to 24 hours. Levels return to normal in about 2 or 3 days.

Who might have a CKMB test?

A CKMB test helps diagnose a heart attack. It is usually given to people experiencing chest pain or weakness immediately after a suspected heart attack and several times in the hours afterward. CK and CKMB levels can also be used to tell whether heart attack treatments such as clot-busting drugs are working.

What does the CKMB test entail?

A blood sample will be taken from a vein in your arm. In some hospitals, a bedside or point-of-care test is available that requires only a finger prick and a few drops of blood. The blood is placed on a strip and positive results are available almost immediately if the CKMB is present in an elevated amount. It takes about 15 minutes to ensure a negative result. The test takes less than a minute.

What do the results of a CKMB test mean?

A high level of CKMB, or an increase in the level between the first and subsequent tests, indicates that there has been some damage to the heart. Because CK can be found in muscles outside of the heart, the ratio of CKMB to total CK is more useful. If the CKMB level is more than 2.5% to 3% of the total CK, the heart muscle is most likely damaged.

What are the limitations of the CKMB test?

CKMB may not be detectable in the blood for three to six hours after the onset of heart attack symptoms; therefore, it is not useful in the very early diagnosis of a heart attack. African Americans and people with a muscular or athletic build have naturally higher CK levels and may have false positive tests (i.e., the test detects a problem when in reality there is none). Strenuous exercise, some medications, or drinking too much alcohol can increase CK levels. Patients with kidney failure may have high CKMB levels without having had a heart attack. In rare cases, chronic muscle disease, low thyroid hormone levels, and alcohol abuse can raise CKMB levels to those seen during a heart attack.


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