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CK-MB

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

At a Glance

Why Get Tested?

To determine if you have had a heart attack and whether certain clot-dissolving drugs are working

When to Get Tested?

If you have chest pain or other signs and symptoms of a heart attack

Sample Required?

A blood sample drawn from a vein in the arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

CK–MB is one of three separate forms (isoenzymes) 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.

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?

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.

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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.

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.

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What does the test result mean?

Looking for reference ranges?

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.

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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.

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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 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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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. 312-315.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006. P. 599.

Engel G, Rockson SG. Rapid diagnosis of myocardial injury with troponin T and CK-MB relative index. Mol Diagn Ther. 2007;11(2): 109-16. Available online at http://www.ncbi.nlm.nih.gov/pubmed/17397247?ordinalpos=3&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum through http://www.ncbi.nlm.nih.gov/pubmed. Accessed February 2009.

Innotrac Diagnsostics. CK-MB Kit. Available online at http://www.innotrac.fi/index.php?main=products&section=cardiac&subsection=ckmb through http://www.innotrac.fi. 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.