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CK

Also known as: Total CK; Creatine phosphokinase; CPK
Formal name: Creatine Kinase
Related tests: CK-MB; Myoglobin; Troponin; Cardiac biomarkers

At a Glance

Why Get Tested?

To determine if you have had a heart attack or if other muscles in your body have been damaged

When to Get Tested?

If you have signs and symptoms of a heart attack (e.g., chest pain); if you have muscle pain or muscular weakness

Sample Required?

A blood sample drawn from a vein in the arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Creatine kinase is an enzyme found in the heart, brain, skeletal muscle, and other tissues. Enzymes are proteins that help cells to perform their normal functions. In muscle and heart cells, most of this energy is used when muscles contract.

There are three different forms of CK in your body; they are referred to as isoenzymes:

  • CK-MM (found in your skeletal muscles and heart),
  • CK-MB (found mostly in your heart),
  • CK-BB (found mostly in your brain).

The small amount of CK that is normally 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.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

Blood levels of CK rise when muscle or heart cells are injured. Your doctor may test for CK if you have chest pain or other signs and symptoms of a heart attack. In the first 4 to 6 hours after a heart attack, the concentration of CK in blood begins to rise. It reaches its highest level in 18 to 24 hours and returns to normal within 2 to 3 days. The amount of CK in blood also rises when skeletal muscles are damaged.

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When is it ordered?

In patients who may have had a heart attack, the CK test will usually be ordered when they arrive at the emergency room and again at intervals of 4-6 hours for a total of three tests. If you have muscle pain or weakness, your doctor may order CK to see if other muscles have been damaged.

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What does the test result mean?

Looking for reference ranges?

A high CK, or one that goes up from the first to the second or later samples, generally indicates that there has been some damage to the heart or other muscles. It can also indicate that your muscles have experienced heavy use. If your doctor suspects a heart attack and your CK is high, she will usually order a more specific test (troponin ) to see if your heart is damaged.

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Is there anything else I should know?

People who have greater muscle mass have higher CK levels than those who don’t, and African-Americans may have higher CK levels than other ethnic groups. 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 a shot (injection), can also increase CK.

Several drugs, including 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. Drinking too much alcohol slightly increases CK as well.

Early pregnancy can decrease CK levels.

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Common Questions

1.  What does heart attack mean?

Heart attack means that some of the muscle in your heart has died. The medical term for this is myocardial infarction (MI). Most commonly, a heart attack starts with a kind of heavy pressure or pain in the chest, often extending into the neck or left arm.  You may have trouble catching your breath, or you may feel weak and break into a cold sweat.

A heart attack usually occurs when one of the blood vessels (called coronary arteries) that bring blood to your heart muscle is blocked. This can happen when a blood clot forms in a blood vessel that is already partially blocked. The partial blockage, which develops over many years, is most often caused by too much fat layered in the wall of the blood vessel (this is often called hardening of the arteries—the medical term for this is atherosclerosis).

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2.  If I have chest pain, does that mean I am having a heart attack? 

Many other problems can cause chest pain, and it is not always possible to tell just from the type of chest pain whether or not you are having a heart attack. Many people have chest pain from straining the muscles in their chest, and chest pain can occur with some lung problems. Chest pain can be a warning sign of hardening of the arteries of the heart (coronary artery disease or CAD). Chest pain that occurs during exercise, hard work, or at times of stress, lasts for a few minutes and goes away with rest is called angina. If the pain lasts longer than just a few minutes, especially if it occurs when you are resting, seek immediate medical attention.

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3.  What are the other heart attack tests? 

Doctors may 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.

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4.  What if I’m not sure I’m having a heart attack? 

If you have prolonged chest pain, especially if it does not go away with rest— or if you have been told you have angina and the drugs you were prescribed do not ease the pain—seek immediate medical attention. Many people who have had a heart attack die without ever having tried to call an ambulance or get to an emergency room.

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Ask a Laboratory Scientist

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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.

Sources Used in Current Review

Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp. 306-309.

MedlinePlus Medical Encyclopedia: CPK. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003503.htm. Accessed February 2009.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.