What is being tested?
CK–MB is one of three forms (or isoenzymes) of the enzyme creatine kinase (CK). CK–MB is found mostly in heart muscle. It rises when there is any damage to heart muscle cells.
How is it used?
CK–MB levels, along with total CK (which measures all the types of CK in the blood together), may be tested in people with chest pain to diagnose whether they have had a heart attack. A high total CK could indicate damage to either the heart or other muscles, but because CK-MB is specific to the heart, a high CK–MB suggests that the damage was due to heart muscle.
When is it requested?
CK-MB is rarely used now; it has been replaced by troponin. However, it may be requested in a person with a high CK to help tell if the damage is to the heart or other muscles.
What does the result mean?
If CK-MB is raised, the heart is the muscle which is likely to be damaged. A high total CK with a low CK-MB suggests that other muscles were damaged.
Is there anything else I should know?
People with other forms of damage to the heart muscle other than a heart attack may have a high CK-MB level, for example people with disease of the heart muscle (cardiomyopathy).
Common questions
Heart attack means that some of the muscle in the heart has been damaged. A medical term for this is acute myocardial infarction (AMI). A heart attack is also known as a type of acute coronary syndrome (ACS). Most commonly, a person having a heart attack feels a kind of heavy pressure or pain in the chest, often extending into the neck or left arm. They may have trouble catching their breath, or may feel weak and break into a cold sweat.
A heart attack usually occurs because one of the blood vessels that bring blood to the heart muscle (called coronary arteries) is blocked. 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 a build-up of fatty-type material in the wall of the blood vessel (this is often called hardening of the arteries — the medical term for this is arteriosclerosis or atherosclerosis).
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 or acid reflux from the stomach.
A form of chest pain known as angina is a heart pain in which there is not serious damage like a heart attack, but it is a warning sign of hardening of the arteries of the heart (the coronary arteries) called coronary artery disease (CAD) or ischaemic heart disease (IHD). Angina occurs during exercise, hard work or at times of stress, lasts for a few minutes and goes away with rest. Angina and heart attack are both forms of acute coronary syndrome (ACS).
Doctors often use more than one test to determine if a person who has chest pain is having a heart attack. Troponin is the best test because the troponin level in the blood can go up when there is no other evidence of a heart attack. Total CK and myoglobin are also used.
What if I am not sure I am 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.
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