Creatine Kinase (CK)

What is creatine kinase (CK)?

Creatine kinase (CK) is an enzyme that mainly exists in your heart and skeletal muscle, with small amounts in your brain. The cells in your skeletal muscles, heart muscles or brain release creatine kinase into your blood when they’re damaged.

An enzyme is a protein that acts as a catalyst to bring about a specific biochemical reaction.

The small amount of CK that’s normally in your blood mainly comes from your skeletal muscles (the muscles that are attached to your bones and tendons). Any condition, injury or event that causes muscle damage and/or interferes with muscle energy production or use increases levels of CK in your blood. For example, intense exercise can increase CK levels. Muscle diseases (myopathies) such as muscular dystrophy can also increase CK levels.

There are three types of CK enzymes:

• CK-MM: Found mostly in your skeletal muscles.
• CK-MB: Found mostly in your heart muscle.
• CK-BB: Found mostly in your brain tissue.

What is a creatine kinase (CK) test?

A creatine kinase (CK) test measures the amount of creatine kinase in your blood.

Elevated CK levels may indicate skeletal muscle, heart or brain damage or degeneration — either chronic (long-term) or acute (short-term).

Other names for a creatine kinase test include:

• CK total.
• CK creatine.
• Phosphokinase CPK.

What is the function of creatine kinase (CK)?

The regular function of creatine kinase (CK) is not really related to what elevated levels of it may indicate in a blood test. CK’s job is to add a phosphate group, a group of natural chemicals, to creatine, a substance in your muscle cells that helps your muscles produce energy. When CK adds phosphates to creatine, it turns the creatine into the high-energy molecule, phosphocreatine, which your body uses to generate energy.

CK gets into your bloodstream when your muscles, heart or brain experience acute damage or chronic degeneration. When your muscles are damaged, the muscle cells break open, and their contents, including creatine kinase, leak into your bloodstream.

What are creatine kinase (CK) tests used for?

Healthcare providers most often use creatine kinase (CK) tests to diagnose and monitor the following muscle issues:

• Muscular diseases.
• Muscular injuries.
• Muscular inflammation (myositis).

Since muscle-related symptoms can be symptoms of several different conditions, your provider may order other tests along with a CK test, including:

• Electrolytes.
• BUN (blood urea nitrogen).
• Creatinine.
• Urine myoglobin.

Muscular diseases

Muscular diseases (myopathies) include:

• Duchenne muscular dystrophy (DMD): This is a rare inherited condition that causes weakness, breakdown and loss of function of your skeletal muscles. It most commonly affects people assigned male at birth.
• Rhabdomyolysis: This condition involves a rapid breakdown of your muscle tissue. It can be caused by a serious injury, muscle disease or other condition.

Muscular injuries

Muscular injuries can result from the following situations:

• Crushed, compressed, torn or strained muscles from accidents or intense exercise.
• Third-degree burns.
• Electrocution.

Muscular inflammation

Types of muscular inflammation (myositis) include:

• Polymyositis: This inflammatory muscle disease causes muscle weakness, usually in the muscles closest to the trunk of your body.
• Dermatomyositis: This is a rare condition that causes muscle weakness and a skin rash.
• Pyomyositis: This is a rare bacterial infection of the muscle that often forms an abscess.

Creatine kinase tests and heart attacks

Healthcare providers sometimes use a creatine kinase (CK) test to help diagnose a heart attack, though not very often. CK testing used to be a common test for heart attacks, but healthcare providers now use another test, called troponin, which is better at detecting heart damage.

Why do I need a creatine kinase (CK) test?

Your healthcare provider may order a creatine kinase (CK) test for you if you have symptoms of a muscular disorder, which include:

• Muscle pain and/or cramps.
• Muscle weakness.
• Balance issues.
• Numbness or tingling.
• Dark urine (pee).

Your provider may also order this test if you’ve had a muscle injury or stroke. CK levels may not peak until up to two days after certain injuries, so you may need to do the test more than once.

Who performs a creatine kinase (CK) test?

A healthcare provider called a phlebotomist usually performs blood draws, which include those for a creatine kinase (CK) blood test, but any healthcare provider who is trained in drawing blood can perform this task. They then send the samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.

How do I prepare for a creatine kinase (CK) test?

In most cases, you don’t need to do anything special to prepare for a creatine kinase (CK) blood test.

If your healthcare provider has ordered a CK test to diagnose a potential muscle disorder, you should limit your exercise to normal activities before the test, since muscle strain from exercise can temporarily increase CK levels in your blood.

What should I expect during my creatine kinase (CK) blood test?

You can expect to experience the following during a blood test, or blood draw:

• You’ll sit in a chair, and a healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
• Once they’ve located a vein, they’ll clean and disinfect the area.
• They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
• After they insert the needle, a small amount of blood will collect in a test tube.
• Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
• They’ll place a bandage over the site, and you’ll be finished.

The entire procedure usually takes less than five minutes.

What should I expect after my creatine kinase (CK) test?

After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.

What are the risks of a creatine kinase (CK) blood test?

Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.

When should I know the results of my creatine kinase (CK) test?

In most cases, you should have your creatine kinase test results within one or two days, though it could take longer.

What do the results of a creatine kinase (CK) test mean?

Blood test reports, including creatine kinase test reports, usually provide the following information:

• The name of the blood test or what was measured in your blood.
• The number or measurement of your blood test result.
• The normal measurement range for that test.
• Information that indicates if your result is normal or abnormal, high or low or positive or negative.

What are normal creatine kinase (CK) levels?

In a healthy adult, normal creatine kinase (CK) levels can vary due to a few factors, including your:

• Sex.
• Race.
• Activity level.

Ranges also vary from lab to lab due to different test methods. Always check the given reference range on your lab report test results. The normal creatine kinase (CK) ranges are generally higher in people assigned male at birth than in people assigned female at birth.

People who have greater muscle mass normally have higher CK levels than those who don’t.

What does a high level of creatine kinase (CK) mean?

Having a high level of creatine kinase (CK), or a rise in levels in subsequent CK tests, generally indicates that you have experienced some recent muscle damage. A CK test can’t indicate which muscle(s) was damaged or the cause of the damage.

Healthcare providers often have you get multiple CK tests to check the progress of your levels. If you have multiple test results that peak and then begin to drop, it usually means your muscle damage has diminished. If your CK levels increase or stay at a persistently high level, it may indicate that you have ongoing muscle damage or muscle degeneration.

If your results show you have higher-than-normal levels of CK, your provider may order tests to check the levels of specific CK enzymes in order to determine the type of muscles affected, including:

• CK-MM enzymes: High levels of CK-MM may mean you have a muscle injury or disease, such as muscular dystrophy or rhabdomyolysis.
• CK-MB enzymes: High levels of CK-MB may mean you have an inflammation in your heart muscle or are having or recently had a heart attack.
• CK-BB enzymes: High levels of CK-MB may mean you have had a stroke or brain injury.

Other causes of increased creatine kinase (CK) levels

Certain conditions and injuries that aren’t directly related to your muscles can cause elevated CK levels, including:

• Hormonal (endocrine) disorders, such as thyroid disease, Addison’s disease or Cushing’s syndrome.
• Prolonged surgeries.
• Seizures.
• Infections (viral, bacterial, fungal or parasitic).
• Connective tissue disorders, such as lupus and rheumatoid arthritis.
• Celiac disease.
• Kidney (renal) failure.
• High fever accompanied by shivering.
• A blood clot.
• Any drug or toxin that interferes with muscle energy production or increases energy requirements.
• Shot injections.

Should I be concerned if I have higher-than-normal creatine kinase (CK) levels?

If your creatine kinase (CK) test results reveal that you have high levels of CK, it doesn't necessarily mean that you have a medical condition. Many other factors, such as exercise, certain medications and shot injections, can temporarily increase your CK levels. There could’ve also been an error in the processing of the test.

When interpreting your results, your healthcare provider will consider several factors, including your current medications, lifestyle and symptoms. They will let you know if you need further testing.

If you have questions about your results, don’t be afraid to talk to your healthcare provider.

When should I call my doctor?

Experiencing muscle pain and weakness is usually temporary. If you’re experiencing prolonged muscle issues, talk to your healthcare provider about your symptoms. They may order a creatine kinase test and other tests to try to determine the cause of your symptoms.

A note from Cleveland Clinic

Seeing an abnormal test result can be stressful. Know that having a high level of creatine kinase doesn’t necessarily mean you have a medical condition and need treatment. Your healthcare provider will let you know if you need to undergo further tests to determine the cause of the abnormal level. Don’t be afraid to ask your provider questions. They’re available to help you.