Also known as: CK MB, CPK MB
Formal name: Creatine Kinase-MB
Why get tested?
To determine if you have had a Heart Attack and whether certain clot-dissolving drugs are working
A blood sample drawn from a vein in the arm
What is being tested?
CK-MB is one of three separate forms of the enzyme creatine kinase (CK). CK-MB is found mostly in heart muscle. It rises when there is damage to heart muscle cells.
How is the sample collected for testing?
A blood sample is taken by needle from the arm.
How is it used?
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 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.
When is it ordered?
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.
What does the test result mean?
NOTE: A standard reference range is not available for this test. Because reference values are dependent on many factors, including patient age, gender, sample population, and test method, numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test. Health.AM strongly recommends that you discuss 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. 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 levels, and alcohol abuse can increase CK-MB, producing changes similar to those seen in a heart attack.
What are the other heart attack tests?
Doctors often use more than one test to determine if a person who has chest pain is having a heart attack. Troponin is generally considered the most accurate test, and CK-MB (the heart isoenzyme of CK) is also highly accurate in detecting damage to the heart, even when there is no other evidence of a heart attack. Myoglobin and creatine kinase almost always rise in patients with a heart attack, but they are less specific - other conditions can also produce an increase in these two tests.
Revision date: July 3, 2011
Last revised: by David A. Scott, M.D.