About the Test
Purpose of the test
A CK test may be used to detect:
- Myositis a group of diseases characterized by inflammation of muscles. Symptoms include difficulty in standing, moving about, swallowing or breathing, and/or muscle pain.
- Myopathies a result of damage due to muscle disorders such as muscular dystrophy
- Rhabdomyolysis the destruction or degeneration of muscle tissueas seen in extreme heat exposure, physical exertion, or crush injuries. Symptoms include muscle cramps, aches, dark urine, and feeling weak or tired. Repeat testing may be required to see if the CK level rises.
- A second heart attack that occurs shortly after the first, though the troponin tests are the main way to diagnose an initial heart attack
A series of CK tests may be used to monitor muscle damage to see if it resolves or continues. CK consists of three subunits (isoenzymes): BB (CK-1; found primarily in brain; when CK-BB is present in the blood, it is released from smooth muscles, including those in intestines, uterus, or placenta), MB (CK-2; found primarily in heart muscle), and MM (CK-3; found primarily in skeletal muscle). Testing for these isoenzymes can be useful when the muscle damage source is unclear.
CK may be ordered along with other blood chemistry tests such as electrolytes, BUN, or creatinine (to evaluate kidney function). Myoglobin is found in muscles and can be released as a result of muscle damage. A urine myoglobin may also be ordered and will reflect the degree of damage – the more myoglobin present the greater the damage. Excess myoglobin can be toxic to kidneys.
What does the test measure?
A CK test measures the amount of CK in the blood. While a small amount of CK is normal, primarily from skeletal muscles, elevated levels might indicate muscle damage.
When should I get this test?
A CK test may be ordered when muscle damage is suspected and at regular intervals to monitor for continued damage. It may be ordered when a muscle disease (myopathy) such as muscular dystrophy is suspected, or if you have experienced physical trauma, such as crushing injuries or extensive burns.
Doctors might also order a CK test if you have ongoing symptoms associated with muscle injury such as:
- Muscle or joint pain
- Muscle weakness
- Frequent falling
- Swelling feet/legs
- Dark urine
CK tests can also be ordered if you take a certain kind of drug, such as a statin, that has been linked with potential muscle damage.
Finding a CK Test
How can I get a CK test?
A CK test can be done at a laboratory when ordered by a physician. Typically, a doctor will order the test for patients who complain of symptoms like prolonged muscle pain or weakness. A CK test is usually not something you would have done without consulting a physician first. You could order CK testing options online to schedule the test at a local laboratory under medical advice.
Can I take the test at home?
Currently, there is no at-home CK testing option. Because of the nature of what is being tested, it’s important to be in consultation with a doctor.
How much does the test cost?
The cost of a CK test will depend on where you have the test done, as well as your health insurance coverage. When it is ordered by a medical professional, it usually is covered by insurance. You may be responsible for a copayment or deductible, however.
For an estimate of what a CK test may cost, it’s best to contact your health insurer or ask the lab.
Taking a CK Test
A CK test is performed by drawing a blood sample from a vein in your arm.
Before the test
While there is no preparation for a CK test, your doctor will most likely ask you not to do any heavy exercise and avoid excessive alcohol intake a few days before the test since either could increase your CK levels temporarily.
During the test
Like other blood tests, you’ll be seated and a phlebotomist will draw a blood sample from a vein in your arm. First, they will apply a rubber tourniquet around the upper part of your arm and may ask you to pump your fist so they can more easily locate a vein. Once they do, they’ll use an alcohol pad to clean the area and let the area dry.
Next, a small needle will be inserted – expect to feel a slight pinch. Blood is collected in a tube, and once the phlebotomist has enough, they will remove the tourniquet, remove the needle, and apply pressure to the area with cotton or gauze. They will then place a bandage on top of the area.
After the test
You generally will not have any restrictions following the CK.
CK Test Results
Receiving test results
CK tests usually take one or two business days to process, but timing can vary depending on where and when the test was performed. With some labs, you may be able to have your results emailed or texted to you, or you can log in to an online patient portal. In other cases, you might call the lab or your doctor to ask about results.
Interpreting test results
CK is reported as U/L – the units (U) of enzyme activity per liter (L) of serum. Normal CK levels can slightly vary from laboratory to laboratory. CK levels do vary depending on gender, race, age, muscle mass, and physical activity. In general, a healthy range in females is 30 to 145 U/L, and for males, it’s 55 to 170 U/L. While males tend to have higher CK levels than females, African Americans tend to have even higher values, whereas age-dependent CK levels have been observed to decrease in older men but not women.
In cases where CK levels are slightly elevated, a doctor may decide to repeat the test after a period of time to see if CK levels go up or down.
For levels that are more concerning, additional testing will likely be ordered. For example, a health care practitioner may order CK isoenzymes or a CK-MB as follow-up tests, to distinguish between the three types (isoenzymes) of CK:
- CK-MB, found primarily in heart muscle
- CK-MM, found chiefly in skeletal muscle
- CK-BB, found originally in the brain; when present in the blood, it is mainly from smooth muscles, including those in intestines, uterus, or placenta.
If you have questions about the results of your CK test, it’s always wise to speak with your doctor. Some things you might want to ask include:
- Is my CK within normal limits?
- Does the elevated level of CK in my blood mean I could have a muscle disease?
- What symptoms could be related to my slightly elevated CK levels?
- What are the next steps to diagnose potential issues?
American Board of Internal Medicine. ABIM Laboratory Test Reference Ranges. Updated January 2022. Accessed September 13, 2022. https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf
National Task Force for Early Identification of Childhood Neuromuscular Disorders. Developmental Delays, Do a CK. Date unknown. Accessed September 13, 2022. https://childmuscleweakness.org/ck-test/
Silberberg C. Rhabdomyolysis. MedlinePlus Medical Encyclopedia. Updated July 27, 2021. Accessed September 13, 2022. https://www.nlm.nih.gov/medlineplus/ency/article/000473.htm
Bethel C, M.D., Master of Public Health. Myopathies. Medscape Review. Updated July 8, 2022. Accessed September 13, 2022. https://emedicine.medscape.com/article/759487-overview
MedlinePlus. Creatine Kinase. Updated December 17, 2020. Accessed September 13, 2020. https://medlineplus.gov/lab-tests/creatine-kinase/
Panteghini M, Bais R. Enzymes. (2008) In Tietz Fundamentals of Clinical Chemistry, 6th r. CA Burtis, ER Aswood, DE Bruns, eds. Saunders:Philadelphia. Chapter 19, pp 317-336.