A blood sample taken from a vein in the arm
Creatine kinase (CK) is an enzyme that occurs in three major forms, called isoenzymes:
- CK-MB (found mostly in heart muscle)
- CK-BB (found mostly in brain)
- CK-MM (found in muscles)
CK–MB rises when there is any damage to heart muscle cells.
How is the sample collected for testing?
A blood sample is taken by needle from the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is required.
How is it used?
CK-MB was once the primary test requested for people who have persistent chest pain to see if they have had a heart attack, have unstable angina or have a problem outside the heart. It has now been largely replaced by the troponin test, which is more specific for damage to the heart. If a troponin test is not available, the CK-MB test is still considered an acceptable substitute.
When is it requested?
The diagnosis of acute heart muscle damage requires an increase in the concentration of CK-MB with time. A blood sample is usually taken on arrival at hospital and a second sample is taken several hours later.
What does the test result mean?
Increased CK-MB concentrations can usually be detected in someone with a heart attack about 4-6 hours after the onset of chest pain. The level of CK-MB peaks approximately at 12-24 hours after the onset of chest pain and then returns to normal within about 48-72 hours.
The internationally agreed definition of heart attack requires not only evidence of a significant increase in CK-MB (or troponin) concentration with time but also evidence of a sudden reduction of heart muscle blood supply (ischaemia) from characteristic symptoms of the acute coronary syndrome (ACS) and new electrocardiogram (ECG) changes or new imaging changes.
Is there anything else I should know?
CK-MB levels may be increased by extensive trauma to skeletal muscles so if, for example, it is suspected that a patient may have had a heart attack that caused a road accident and resulted in muscle injury, a troponin test should be requested, as the concentration of CK within the bloodstream may be increased as a result of damage to the body during the road accident.
What does heart attack mean?
Heart attack means that some of the muscle in your heart has died. A 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 breathing, or you may feel weak and break into a cold sweat.
A heart attack usually occurs because of a blockage in one of the blood vessels (called coronary arteries) that bring blood to your heart muscle. This happens when a blood clot forms in a blood vessel that is already partially blocked. The partial blockage, which happens gradually over many years, is usually 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).
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 called coronary artery disease (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.
What are the other tests for a heart attack?
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.