How is it used?When is it ordered?What does the test result mean?Is there anything else I should know?
CK–MB levels, along with
total CK, are tested in persons who have chest pain to diagnose whether they have had a
heart attack. Since a high total CK could indicate damage to either the heart or other muscles, CK–MB helps to distinguish between these two sources.
If your doctor thinks that you have had a heart attack and gives you a “clot-dissolving” drug, CK–MB can help your doctor tell if the drug worked. When the clot dissolves, CK–MB tends to rise and fall faster. By measuring CK–MB in blood several times, your doctor can usually tell whether the drug has been effective.
CK-MB is usually ordered along with
total CK in persons with chest pain to determine whether the pain is due to a
heart attack. It may also be ordered in a person with a high CK to determine whether damage is to the heart or other muscles.
Increased CK-MB can usually be detected in heart attack patients about 3-4 hours after onset of chest pain. The concentration of CK-MB peaks in 18-24 hours and then returns to normal within 72 hours.
Although CK-MB is a very good test, it has been largely replaced by troponin, which is more specific for damage to the heart.
What does the test result mean?NOTE: This test has no single number that identifies an abnormal result.
Your lab report (see a sample report) should include
a range of numbers (reference range) that identifies what is expected for you based on
your age, sex, and the method used in that laboratory. You can find more information
about expected results at Reference Ranges
and What They Mean. Lab Tests Online strongly recommends that you discuss the meaning of your test results with your doctor.
If the value of CK-MB is elevated and the ratio of CK–MB to total CK (relative index) is more than 2.5–3, it is likely that the heart was damaged. A high CK with a relative index below this value suggests that skeletal muscles were damaged.
Is there anything else I should know?
Severe injury to skeletal muscle can be significant enough to raise CK–MB levels above normal, but such injury doesn’t usually cause a high relative index. Strenuous exercise may also increase both
CK and CK-MB.
If your doctor suspects injury to both heart muscle and skeletal muscle, troponin is a more accurate test for identifying a heart attack.
Sometimes persons who are having trouble breathing have to use their chest muscles. Chest muscles have more CK–MB than other muscles, which would raise the amount of CK–MB in the blood.
Persons whose kidneys have failed can also have high CK–MB levels without having had a heart attack. Rarely, chronic muscle disease, low thyroid hormone (T3, T4, TSH) levels, and alcohol abuse can increase CK–MB, producing changes similar to those seen in a heart attack.
