What Is the CPK Enzyme Test?

Medically Reviewed by Poonam Sachdev on November 10, 2022
5 min read

Your doctor may recommend the creatine phosphokinase (CPK) test if there's a need to measure CPK enzyme levels in your blood. The cells in your body require this creatine kinase enzyme to generate energy. 

If the test finds high amounts of CPK in your blood, it could be a sign of some sort of injury or stress in your muscles or heart. However, the enzyme levels can also increase due to factors like vigorous exercise and certain medications. So, you shouldn't worry if your CPK enzyme test result comes out positive. Rather, wait for your doctor to ascertain if you have any underlying medical condition and begin the treatment accordingly.

Creatine phosphokinase is an enzyme — a protein that brings about specific chemical changes in your body. 

As its name suggests, the function of the CPK enzyme is to add a phosphate group to creatine, a naturally occurring chemical found in your muscle cells. As a result, creatine turns into phosphocreatine — a high-energy substance used by your body to generate energy.

While creatine kinase is mostly found in your skeletal muscles and heart muscles, small amounts of it also exist in your brain. Based on where this enzyme is found inside the body, it's grouped into these types:

  • CPK-1 (or CPK-BB): Mainly found in the lungs and brain 
  • CPK-2 (or CPK-MB): Mainly found in the heart
  • CPK-3 (or CPK-MM): Mainly found in the skeletal muscles

When the tissues of your skeletal muscles or the heart get damaged or start degenerating, the cells inside them break open. This causes the contents of these cells — including the CPK enzyme — to leak into your blood. This is why doctors consider high levels of creatine phosphokinase in your blood to be a sign of stress or injury to your heart, muscle, or brain tissue. Among these, an injury to the muscle tissue is most likely.

The CPK enzyme test helps to measure the levels of creatine phosphokinase in your blood. Other names for this test are:

  • CK creatine
  • CK total
  • Phosphokinase CPK

Determining your CPK levels requires a blood sample. This blood is likely taken from a vein in your arm. If this test is done while you're staying in a hospital as a patient, then it may be repeated over the next 2 or 3 days.

During this procedure, you could feel slight pain, stinging, or a pricking sensation as the needle is inserted into your vein. You may have a throbbing sensation that can last the whole day.

If the test finds high total CPK levels in your blood, this could mean that either acute (short-term) or chronic (long-term) degeneration or damage has happened to your heart, brain, or skeletal muscle. Keep in mind that in case of certain injuries, the CPK enzyme levels peak only after two days have passed. In such cases, you may be asked to get the test done more than once.

Once the final CPK enzyme test is done, your doctor could recommend the CPK isoenzymes test to find out which type of CPK isoenzyme is highest in your blood. This could help them pinpoint exactly which tissue is damaged in your body.

Creatine kinase levels usually reflect the condition of your skeletal muscles, heart, or brain. So, this test is recommended when you face any problems related to these organs. 

For example, if you show signs of a heart attack like chest pain, the doctor may suggest a CPK enzyme test along with others. Your CK-MB levels as well as the way your CPK levels rise and fall could help the doctor diagnose if it's actually a heart attack.

Since creatine phosphokinase is also found in your skeletal muscles, the test could help to detect muscle injury and muscle-related problems like polymyositis and dermatomyositis. Your doctor may ask you to get a CPK test if you have symptoms like:

  • Muscle pain
  • Muscle weakness
  • Muscle cramps
  • Dark urine
  • Tingling or numbness
  • Balance problems

Usually, the normal range of CPK levels falls anywhere between 10 to 120 micrograms per liter (mcg/l).

This range can vary from lab to lab because each lab uses its own measurements and test methods. It's best to check your result with the given reference range provided by the lab. 

As a healthy adult, your creatine kinase levels could also vary based on your race, gender, and activity level. For example, the average CPK ranges are usually higher in those born with male sex organs than those assigned female at birth. Similarly, the levels of this enzyme are also higher in those who have more muscle mass compared to those who don't.

Higher-than-normal CPK enzyme levels could be a sign of problems associated with your heart, brain, or skeletal muscles. Such problems could be seen in people having:

Brain and lung issues (indicated by abnormally high CPK-1 levels):

  • Seizure
  • Brain injury or stroke
  • Convulsions
  • Brain cancer 
  • Delirium tremens 
  • Lung tissue death (pulmonary infarction)
  • Electric shock

Heart issues (indicated by abnormally high CPK-2 levels):

  • Heart attack
  • Open heart surgery
  • Heart injury (for example, after a road accident)
  • Heart muscle inflammation (myocarditis)
  • Electrical injuries

Muscle injury or muscle stress (indicated by abnormally high CPK-3 levels):

  • Muscular dystrophy
  • Myopathy
  • Crash injuries
  • Drug-related muscle damage 
  • Muscle damage after a long period of immobility (rhabdomyolysis)
  • Dermatomyositis or polymyositis

Other factors that could cause high CPK levels despite not directly affecting your muscles, heart, or brain include:

  • Hypothyroidism
  • Hyperthyroidism
  • Addison’s disease
  • Kidney failure
  • Microbial infections
  • Cushing's syndrome
  • Celiac disease
  • Autoimmune disorders like rheumatoid arthritis or lupus
  • Heavy exercise
  • Injections
  • Prolonged surgery
  • Intake of any toxin or drug that interferes with energy production in your muscles

You don't need to prepare in any special way before taking a CPK test. Just make sure to let your doctor know about the drugs you're taking. This is because some medications can affect your CPK enzyme test results.

For example, taking these drugs before the test could cause your test results to show high CPK levels:

Having high CPK levels in your test results could mean many things. It could be a temporary result of a vigorous exercise routine or injections you have had. The result could also occur due to an error in the processing of the test. 

Your doctor would consider all these factors, including your symptoms and lifestyle, as well as determine if any further tests are needed. Once all the tests are done, your doctor would interpret the results and determine the underlying cause of your problem. If necessary, your doctor will recommend a proper treatment plan. Follow it correctly to reduce the risk of any complications.