Creatine Kinase
Also written as: CK, CPK, creatine phosphokinase, total CK
An enzyme from muscle, released into the blood when muscle is worked hard or injured.
What it measures
The activity of creatine kinase, an enzyme concentrated in skeletal muscle, heart muscle, and brain tissue. It leaks into the blood when muscle cells are stressed or damaged, so the blood level reflects recent muscle strain or injury.
Why a doctor orders it
Commonly ordered when muscle aches, weakness, or dark urine raise the question of muscle injury. It is also used to check on people taking statin cholesterol medicines, which occasionally irritate muscle, and after falls, seizures, or prolonged immobility.
What is generally associated with a higher result
Broadly associated with muscle injury of any kind, from strenuous exercise and bruising falls to inflammatory muscle conditions. A single hard workout can raise it substantially for several days. Very high levels are associated with rhabdomyolysis, a rapid breakdown of muscle tissue.
What is generally associated with a lower result
Broadly associated with lower muscle mass or a sedentary lifestyle. Low values are generally not pursued.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Exercise in the past several days, even one unusually hard session
- Recent falls, bruises, or injections into a muscle
- Muscle mass - muscular people tend to run higher at baseline
- Ancestry - typical baseline levels differ between populations
- Statins and some other common medicines
Questions to take to your appointment
- How long should I avoid hard exercise before this is drawn again?
- Could a medicine I take, such as a statin, be contributing to the level?
- Is my baseline likely to run high because of my build or ancestry?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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