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Creatine Kinase with Isoenzymes (Blood)

Does this test have other names?

Creatine kinase, creatine phosphokinase with isoenzymes, CK, CPK, CK-MM, CK-MB, CK-BB

What is this test?

This test is used to find damage to muscles in your body, including your heart muscle.

Creatine kinase (CK) is an enzyme found in your muscles. Enzymes are proteins that help your body's cells do their jobs. The level of the CK enzymes rises when you have damage to muscle cells in your body.

The three types of CK are called isoenzymes. They are:

  • CK-MM, which is found in your skeletal muscle and heart

  • CK-MB, which is found in the heart and rises when heart muscle is damaged

  • CK-BB, which is found mostly in your brain

A general creatine kinase test can tell whether there is damage to your body's muscles. Going a step further, the creatine kinase with isoenzymes test may help pinpoint where the damage has taken place.  

Why do I need this test?

You may need this test if you have:

  • Symptoms of a heart attack, such as chest pain

  • Muscle weakness, pain, or inflammation

Your doctor may also order this test if you have been diagnosed with a muscular disorder and he or she wants to monitor your body's response to treatment. 

What other tests might I have along with this test?

If your doctor suspects a heart attack, he or she will also likely order:

  • Troponin blood test. It's like a CK test but more sensitive and specific.

  • Electrocardiogram, or ECG, to measure the electrical activity of your heart.

Several other muscle enzymes may be tested along with CK. Comparing CK test results with the results of these other muscle enzyme tests can help your doctor better diagnose and treat you. The other muscle enzymes that may be tested are:

  • Aldolase, found mostly in skeletal muscle, liver, and brain

  • Lactate dehydrogenase, found throughout the body

  • Aminotransferases, found throughout the body but often used to detect liver disorders 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

The results for this test include both a general CK measurement and a percentage for each of the three isoenzymes. An elevated CK level could be a sign of muscle damage in your heart or elsewhere.

The normal range for the general CK measurement depends on your age and gender. Generally, the normal range is:

  • 55 to 170 units per liter (L) for adult males

  • 30 to 135 units/L for adult females

  • 68 to 580 units/L for newborns 

Elevated levels of the three isoenzymes mean different things:

  • CK-MM generally rises in response to muscle damage in your heart, brain, or skeleton after a crush injury, seizures, muscular dystrophy, muscle inflammation, or another skeletal muscle disorder.

  • CK-MB generally rises in response to a heart attack, inflammation of the heart muscle, muscular dystrophy, and other problems related to the heart.

  • CK-BB tends to rise in response to a brain injury, meningitis, abnormal cell growth, severe shock, stroke, hypothermia, or restricted blood flow to the bowel.

The normal levels for the three isoenzymes of creatine kinase are:

  • CK-MM: 100 percent

  • CK-MB:  0 percent

  • CK-BB:  0 percent 

How is this test done?

The test requires a blood sample, which is drawn by putting a needle into a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

Intense physical exercise, such as running a marathon, within a day or two of the test can lead to higher CK-MB levels.

Skeletal muscle damage, especially blunt trauma to the muscles, and cocaine abuse can also increase your levels of CK-MB, which is found mostly in the heart.

Drinking too much alcohol can also raise your CK levels. In some cases, people with low thyroid hormone levels and alcohol abuse may also have elevated CK-MB levels.

Certain medications can also increase levels. 

How do I get ready for this test?

You don't need to prepare for this test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.