The creatine kinase test is a blood test that measures the levels of an enzyme called creatine kinase. This enzyme supports energy production in the body and is especially important for muscle and brain health.
The creatine kinase test is used to diagnose and monitor several medical conditions, such as those that damage the heart, brain, and skeletal muscles.
Creatine phosphokinase (CPK), also known as creatine kinase (CK), is a type of enzyme. Enzymes are proteins that catalyze (speed up) chemical reactions in your body.
CK plays an important role in energy production because it is responsible for the creation of adenosine triphosphate (ATP). ATP is the source of energy for tissues and cells throughout the body, especially skeletal muscle and the brain.
CK is concentrated in the cells that make up your brain and skeletal and heart muscles. There are three types of CK enzymes:
- CPK-MB (cardiac muscle): CPK-MB is mainly found in your heart muscle.
- CPK-MM (skeletal muscles): CPK-MM is mainly found in your skeletal muscles.
- CK-BB (brain): CK-BB is mainly found in your brain tissue.
There is usually only a small amount of CK in the bloodstream due to the normal breakdown of muscle tissue caused by everyday wear and tear, such as exercise and walking.
When significant damage occurs to areas where CK is stored, such as the muscles, heart, and brain, blood levels of CK become elevated. For example, when a person has a heart attack, CK levels rise due to damage and death of heart cells. This is why CK tests can help diagnose muscle damage and other serious health conditions.
The CK test is a blood test. During this test, a healthcare professional uses a needle to take a sample of blood from a vein in your arm. The blood sample is then sent to a laboratory for analysis and assessment of CK levels.
The amount of CK in the blood is expressed in units (U) of enzyme activity per liter (L) of serum. Normal CK levels vary depending on factors such as gender, body composition, race, and physical activity levels.
Blacks have higher CK activity than whites because of differences in CK production or clearance. Men tend to have higher CK levels than women due to their greater muscle mass.
The normal range for CK in Caucasian adults is 46-171 U/L for men and 34-145 U/L for women when using the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) testing procedure. This range varies depending on the test methods and laboratories used.
Although high CK levels are not always cause for concern, elevated levels can indicate several injuries and medical conditions, such as muscle damage and muscle-related diseases.
The CK test is used to diagnose injuries and medical conditions, such as:
- Muscle injuries: CK is released when skeletal muscle is injured. Trauma, severe burns and extreme exercise can lead to muscle damage.
- Muscle diseases: When muscle tissue breaks down, it releases compounds such as electrolytes and proteins, including CK, into the blood. The CK test can help diagnose muscle diseases such as muscular dystrophy, rhabdomyolysisand myositis.
- myositis: Myositis is the name given to a group of rare conditions that cause muscle weakness due to inflammation. Myositis is an autoimmune disease, meaning the immune system attacks muscle tissue, causing CK to leak into the bloodstream.
- Muscular dystrophy (MS): Muscular dystrophy is a group of diseases that cause progressive muscle weakness and wasting. The level of CK is significantly elevated in all types of muscular dystrophy.
- rhabdomyolysis: Rhabdomyolysis is a medical condition characterized by the rapid breakdown of muscle tissue, which causes an increase in CK in the bloodstream. A CK level greater than 1,000 IU/L indicates rhabdomyolysis, and levels greater than 5,000 IU/L indicate severe rhabdomyolysis. Trauma, extreme exercise, crush injuries, infections, muscle diseases, and certain medications can cause rhabdomyolysis.
In addition to the medical conditions listed above, CK is sometimes used to diagnose heart attacks.
The troponin test, which measures levels of the troponin protein in the blood, is generally considered a better marker for diagnosing a heart attack. However, healthcare professionals can also use CK to detect a heart attack.
Troponin is more specific and sensitive than CK, because cardiac troponin increases only when heart muscle damage occurs. Conversely, increased CK levels may indicate muscle damage in other areas.
In some cases, CK tests can be used to measure the severity of a stroke and to predict the chance of a repeat stroke.
Blood CK levels depend on many factors, such as age, sex, race, muscle mass, and physical activity. For this reason, it is necessary to interpret the results of the CK test with the help of a health professional.
The CK test is usually used in conjunction with other tests, including other muscle enzyme tests, to diagnose a medical condition. If your CK levels come back elevated, you may have some type of muscle damage. Your healthcare provider may order more blood and additional testing to help them determine whether or not you have an injury or medical condition.
To narrow down the type of muscle damage, a healthcare provider may order a CK isoenzyme test, which measures different types of CK in the blood. High levels of the CK-MM enzyme indicate damage to your skeletal muscles, while high levels of the CK-MB enzyme can be a sign of damage to your heart muscle.
Remember that CK levels can fluctuate, so your healthcare provider may recommend testing them more than once to assess muscle damage.
A CK test is usually ordered by a health care provider in an emergency setting, such as a hospital or urgent care center. A provider may also order this test during a physical exam if a person has experienced trauma, has a certain medical condition, or has symptoms that may indicate muscle damage.
CK levels are often checked as part of trauma protocols in intensive care units (ICUs) when people have fractures or injured blood vessels caused by blunt force trauma or penetration.
In a hospital setting, your healthcare team may perform a CK test if you have had any of the following:
- Serious injury or serious trauma
- Significant burns
- Traumatic brain injury or stroke
People who take certain medications (eg, statins) or have medical conditions (eg, muscle disorders such as muscular dystrophy) will also need to have their CK levels monitored regularly.
Symptoms
Although not always indicative of muscle damage, the following symptoms may be a sign that a CK test may be needed:
- Muscle pain
- Muscle cramps
- Muscle weakness
- Coordination or balance issues
- Numbness or tingling in the extremities (hands and feet)
- Dark colored urine
- Swollen legs or feet
Some of these symptoms (eg normal muscle soreness caused by exercise) are not always cause for concern. However, if you have extreme or prolonged muscle pain or any of the other symptoms listed above, it’s best to make an appointment with your doctor. If necessary, they will recommend appropriate testing, potentially including a CK test.
Talk to your doctor if you have any questions about CK or CK tests. They can provide more information about CK testing and determine if it is appropriate based on your medical history and symptoms.
Creatine kinase (CK) is an enzyme found in the muscles, heart and brain. It helps support energy production in these areas.
The CK test is a blood test that measures CK levels. It is used to diagnose and monitor several medical conditions, such as trauma-related muscle injuries and muscular dystrophy.
Your doctor may order a CK test if you have severe or persistent muscle pain, muscle weakness, balance problems, or tingling in your hands and feet. If you have a muscle disorder, your doctor will likely test your CK levels regularly.