Creatine kinase (CK) is an important protein in muscle cells. It is also found in the heart, brain, and other tissues, but at lower levels. Increased amounts of CK are released into the blood when there is muscle damage. CK levels can also be increased when there is heart muscle damage, for example with a myocardial infarction. This test measures the amount of creatine kinase in the blood.
Persistently high CK levels can be found in many muscular dystrophies as the CK is released as the muscle cells break down. However, levels are not increased in all muscular dystrophies. In an individual with a muscular dystrophy, CK levels may be raised before weakness is evident clinically. In inflammatory muscle conditions CK levels can also be very elevated.
In addition, there are many other conditions where CK levels are found to be elevated, including after strenuous exercise and trauma and in some endocrine disorders. Certain medication may also increase CK levels. Thus an elevated CK level does not confirm a diagnosis of a muscular dystrophy.