Creatine Kinase (CK) Test
At a Glance
Why Get Tested?
To find out if you have had a heart attack and if other muscles in your body have been damaged
When to Get Tested?
If you have chest pain or muscle pain and weakness
Sample Required?
A blood sample taken from a vein in the arm
The Test Sample
What is being tested?
Creatine kinase is an enzyme found in the heart, brain, and skeletal muscle. Enzymes are proteins that help cells perform their normal functions. In muscle, for example, CK helps cells make the energy needed to move. CK occurs in three major forms, called isoenzymes:
- CK-MB (found mostly in your heart muscle),
- CK-BB (found mostly in your brain), and
- CK-MM (found in your heart and other muscles).
CK in the blood comes mainly from your muscles. The CK in your brain almost never gets into the blood.
How is the sample collected for testing?
A blood sample is taken by needle from the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
The Test
How is it used?
Blood levels of CK rise when your muscle or heart cells are injured. Your doctor may request measurement of CK (along with tests for other substances, particularly the CK–MB form) if you have chest pain to see if you may have had a heart attack. In the first 4 to 6 hours after a heart attack, CK in blood begins to rise. It reaches its highest level after about 18 to 24 hours, and returns to normal in about 2 to 3 days. The test for CK can also indicate if your other muscles are damaged.
When is it requested?
What does the test result mean?
A high CK, or one that has increased in concentration, usually indicates that there has been some damage to the heart or other muscle. It can also indicate that your muscles have been used heavily, for example if you have exercised excessively. If your doctor suspects a heart attack and your CK is high, they will usually also request a test which is a better indicator of heart muscle damage (troponin or less commonly, CK-MB).
Is there anything else I should know?
People who have greater muscle mass have higher CK levels (for example a young fit male will have more muscle mass and hence a higher CK level than an elderly female), and Afro-Caribbeans may have higher CK levels than other ethnic groups. Raised CK levels can also be seen in those with some diseases of the thyroid gland (hypothyroidism). Very heavy exercise (such as in weight lifting, contact sports, or long exercise sessions) can also increase CK.
Other forms of muscle damage, such as from a fall, a car accident, surgery, or after an injection, can also increase CK. Drinking too much alcohol slightly increases CK. Rarely, some drugs, particularly cholesterol-lowering drugs (statins), can damage muscle and increase CK. If you are taking one of these drugs, let your doctor know if you experience any muscle pain or weakness. Early pregnancy can decrease CK levels.
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
