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CK-MB


At a Glance

Why Get Tested?

To distinguish between skeletal muscle and heart muscle damage; sometimes to determine if you have had a heart attack (if the troponin test is not available); sometimes to detect a second or subsequent heart attack or to monitor for additional heart damage

When to Get Tested?

When you have an increased creatine kinase (CK) level and the healthcare practitioner wants to determine whether it is due to skeletal or heart muscle damage; when it is suspected that you have had a second heart attack or have ongoing heart damage

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

Creatine kinase-MB (CK-MB) is a form of an enzyme found primarily in heart muscle cells. This test measures CK-MB in the blood.

CK-MB is one of three forms (isoenzymes) of the enzyme creatine kinase (CK). These isoenzymes include:

  • CK-MM (found in skeletal muscles and the heart)
  • CK-MB (found mostly in the heart, but small amounts found in skeletal muscles)
  • CK-BB (found mostly in the brain and smooth muscle, such as the intestines and uterus)

CK is released from muscle cells and is detectable in the blood whenever there is muscle damage. The small amount of CK that is normally in the blood is primarily CK-MM. CK-BB almost never gets into the blood, and CK-MB will typically only be present in significant amounts when the heart is damaged. A CK test measures the total level but does not distinguish between the three isoenzymes. When there is an increased amount of CK present in the blood, the CK-MB test can be used to determine whether it is due to heart damage or is more likely to be related to skeletal muscle injury.

How is the sample collected for testing?

A blood sample is taken by needle from a vein in the arm.

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

No test preparation is usually needed because the test is done in emergency care.

The Test

How is it used?

A creatine kinase-MB (CK-MB) test may be used as a follow-up test to an elevated creatine kinase (CK) in order to determine whether the increase is due to heart damage or skeletal muscle damage. The test is most likely to be ordered if a person has chest pain or if a person's diagnosis is unclear, such as if a person has nonspecific symptoms like shortness of breath, extreme fatigue, dizziness, or nausea.

CK and CK-MB were once the primary tests ordered to detect and monitor heart attacks, but they have now been largely replaced by the troponin test, which is more specific for damage to the heart.

Sometimes, the CK test may be used if a heart attack is suspected and a troponin test is not available. In this case, when CK is elevated, a CK-MB test may be used as a follow-up test to determine whether the increase is due to heart damage or skeletal muscle damage.

When is it ordered?

CK-MB is usually ordered along with or following an elevated total CK when a person has chest pain and a healthcare practitioner wants to determine whether the pain is due to a heart attack. It is typically ordered for this purpose when the more specific troponin test is not available. A CK-MB may also be ordered when a person has a high CK to determine whether the muscle damage detected is to the heart or other muscles.

Increased CK-MB can usually be detected in someone with a heart attack about 3-6 hours after the onset of chest pain. The level of CK-MB peaks in 12-24 hours and then returns to normal within about 48-72 hours. If there is a second heart attack or ongoing damage, then levels may rise again and/or stay elevated longer.

What does the test result mean?

CK-MB is normally undetectable or very low in the blood.

Chest pain and increased CK levels plus elevated CK-MB indicate that it is likely that a person has recently had a heart attack. Levels that drop, then rise again may indicate a second heart attack and/or ongoing heart damage.

If CK-MB is elevated and the ratio of CK-MB to total CK (relative index) is more than 2.5-3, then it is likely that the heart was damaged. A high CK with a relative index below this value suggests that skeletal muscles were damaged. (For more, see Common Questions #3.)

Any kind of heart muscle damage can cause an increase in CK and CK-MB, including physical damage from trauma, surgery, inflammation, and decreased oxygen (ischemia). Strenuous exercise may also increase both CK and CK-MB, but usually with a lower relative index.

Kidney failure can cause a high CK-MB level.

Rarely, chronic muscle disease, low thyroid hormone (T3, T4) levels, and alcohol abuse can increase CK-MB.

Is there anything else I should know?

Since CK-MB is also present in small quantities in skeletal muscle, significant damage to skeletal muscles can also increase the CK-MB level. If both skeletal and heart muscles are damaged, the presence of CK-MB due to a heart attack could be masked.



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