Summary

• CK or creatine kinase is an enzyme that is released into the blood from muscles, heart and brain when they are damaged.
• Measuring CK levels in the blood can help diagnose conditions linked to muscle damage.
• Although in the past the CK test was used to diagnose a heart attack, it has been replaced by troponin T or troponin I tests.

What is creatine kinase?

CK or creatine kinase is an enzyme that helps produce energy in muscles. Enzymes are substances that help speed up chemical reactions in the body. CK mostly works in skeletal muscles (the muscles that are attached to bones and tendons) and the heart (which is also a muscle) but it is also found in small amounts in other parts of the body, including the brain and the gut.

Normally, levels of CK in the blood are low but if your muscles or your heart are damaged, muscle cells break open and CK leaks into your blood. This means that CK levels rise. Measuring the amount of CK in your blood can help diagnose conditions associated with muscle damage. This could be due to injury, serious burns or surgery, or to muscle disorders such as muscular dystrophy.

Why get tested?

A CK test is ordered when muscle damage is suspected and then repeated at regular intervals afterwards to check for improvement. Once damage stops and cells stop leaking CK, the level of CK in the blood starts to go back to normal.

Natural wear and tear cause muscles to release CK, so it is normal to detect some CK in the blood of healthy people. People with bigger muscles, such as body builders, will have a higher normal CK level than other people, such as older women.

In the past, CK was used in diagnosing heart attack but other tests such as troponin T and troponin I have largely replaced it.

Almost everyone with a neuromuscular disorder will have a CK test. Neuromuscular disorders affect the nerves that control muscles. If you have one of these disorders CK test can be used to investigate a possible muscle problem before other symptoms occur and to find out if your muscle weakness is caused by a muscle or a nerve problem. It can also help to differentiate between different types of disorders. It is especially useful for monitoring the progress of neuromuscular diseases and assessing the effectiveness of treatment. The CK test is also used to check infants for early diagnosis of certain disorders, such as Duchenne muscular dystrophy.

A CK test may also be ordered if:

• you have had a stroke or traumatic brain injury.
• in diagnosing myositis, a rare group of diseases that cause inflammation of the muscles.
• to help diagnose Rhabdomyolysis, a rare but serious condition in which your muscles break down due to extreme heat exposure, physical exertion, or crush injuries.

Some medications, particularly cholesterol-lowering statins, can damage muscles and increase CK. If you are taking one of these medications, let your doctor know if you experience any muscle pain or weakness.

Infections, such as influenza, can damage muscles and cause a higher-than-normal CK level. Higher CK levels have also been associated with worse outcomes for people with COVID-19 infections.

What the CK test measures

When a CK test is requested, it measures the total of three different forms of CK in your blood and is sometimes referred to as a 'total CK' test. The three forms of CK are:

• CK-MM (found in the heart and skeletal muscle and makes up most of the CK in the blood)
• CK-MB (found mostly in heart muscle)
• CK-BB (found mostly in the brain)

Although the three forms of CK can provide more information, they are rarely measured separately today as there are more specific tests available. These newer tests can indicate the location and cause of muscle damage, making them more efficient for diagnosis and treatment. For example, troponin T or troponin I are better markers of heart muscle damage than CK-MB.

Having the test

Sample

Blood

Preparation

No special preparation is needed, although you should avoid heavy exercise and not drink large amounts of alcohol for a few days before the test as these can affect the results.

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Having a CK level that is significantly higher than normal indicates some muscle damage. Because it can take up to two days after muscle injuries for CK levels to peak, multiple CK tests may be needed to track any changes.

A high CK level in your blood usually means there has been damage to muscles. Increasing CK levels suggest ongoing muscle damage.

High levels indicate only that there is muscle damage, and do not show the location of the damage or cause. If the reason for the high CK level is not clear, your doctor will order additional tests to work out where it is coming from.

If there is muscle damage then myoglobin, a protein found in muscles, will also be high. This is detected by a urine myoglobin test and a high level will indicate muscle damage. High myoglobin levels can damage your kidneys. Often kidney function tests will also be done.

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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