What is a creatine kinase (CK) test?

This test measures the amount of creatine kinase (CK) in a sample of your blood. CK is also called creatine phosphokinase (CPK).

CK is an enzyme. An enzyme is a protein that speeds up certain chemical reactions in your body. CK helps make energy. Most of the CK in your body is in your skeletal muscles. These are the muscles you use to move. You also have CK in your heart muscle and small amounts in your brain.

Normally, a small amount of CK gets into your blood from the usual wear and tear on your muscles. But if your muscles, heart, or brain tissues are damaged, larger amounts of CK leak out of your cells into your bloodstream.

A CK test is mainly used to help diagnose and monitor injuries and diseases that damage skeletal muscles and cause high levels of CK in your blood. But it may also be used for conditions that damage the heart muscle and the brain.

Other names: CK, total CK, creatine phosphokinase, CPK

What is it used for?

A CK test is most often used to help diagnose and monitor:

• Muscle injuries, including injuries from accidents, serious burns, or extreme exercise.
• Muscle diseases, including:
  • Muscular dystrophy, a group of inherited muscle diseases that weaken muscles over time.
  • Rhabdomyolysis, or "rhabdo," a rapid breakdown of muscle tissue which releases proteins and electrolytes into the blood. This uncommon condition can damage the heart and lead to sudden kidney failure. Rhabdo has many causes, including serious injuries, working in very hot places, overusing muscles, and certain medicines and medical conditions that affect the muscles.
  • Myositis, a group of rare diseases that involve long-term muscle inflammation (swelling), weakness, and sometimes pain.

In certain cases, a CK test may be used to help diagnose a heart attack. Another blood test, called a troponin test is used more often. That's because troponin testing is better at finding damage to the heart muscle from a heart attack.

If you've had a stroke, a CK test may be done to find out how severe it was. The test may also help predict the chance that you may have another stroke.

Why do I need a CK test?

You may need a CK test if you have symptoms of a muscular disorder. These include:

• Muscle pain and/or cramps
• Muscle weakness
• Balance problems and/or falling a lot
• Numbness or tingling
• Dark colored urine (pee)
• Swollen legs or feet

You may also need this test if you:

• Have had an injury that crushed or tore your muscles
• Have had serious burns
• Take certain medicines that may cause muscle damage, such as statins to lower blood cholesterol
• Have had a stroke or traumatic brain injury (TBI)

What happens during a CK test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a CK test. To help make sure your results are accurate, your provider may ask you to avoid intense exercise and drinking alcohol for a few days before your test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Normal CK levels for you will depend on:

• Your age, sex, and race
• How much muscle you have
• How physically active you are

If your CK level is higher than normal, it usually means you have some type of muscle damage. CK levels may not reach their highest until up to two days after certain injuries. So, you may have more than one CK test to see if your levels go up or down. CK levels that stay high or increase may mean that muscle damage is continuing to happen.

But a CK test result can't show where the damage is or what's causing it. Your provider will consider your symptoms and medical history to understand what your test results mean.

If the source of high or increasing CK levels isn't clear, you may need a more specific type of CK test to find out if the CK is coming from your muscles, heart, or brain. This more specific test is called a CK isoenzymes test.

A CK isoenzymes test measures three different types of CK:

• High levels of CK-MM enzymes are most likely from damage to your skeletal muscles. The damage may be from disease, sudden injury, certain medicines, or recent intense exercise.
• High levels of CK-MB enzymes are most likely from damage to your heart muscle. The damage is often caused by heart attack or inflammation in your heart muscle (myocarditis). But other conditions can also cause high levels of CK-MB, such as:
  • A blood clot in the lung
  • Heart surgery
  • Congestive heart failure
  • Hypothyroidism
  • Kidney failure
• Higher than normal CK-BB enzymes may mean you had a stroke or brain injury. But conditions that affect smooth muscles can also increase CK-BB levels. Smooth muscles are muscles you can't control, for example, the muscles in your digestive system.

To diagnose the condition causing high CK levels, you may need other types of tests, too. The tests you have will depend on which types of CK enzymes are high as well as your symptoms and medical history.

If you have questions about any of your test results or diagnosis, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.