Creatine kinase

Creatine kinase (CK) is an enzyme which catalyses the formation of creatine phosphate from creatine. Creatine phosphate is the main energy source in muscle, and so this enzyme is abundant in skeletal muscle.

There are three isotypes of CK. CK-MM is mostly found in skeletal muscle. CK-MB is mostly found in myocardium (but only accounts for 30% of CK here). CK-BB is the dominant form in smooth muscle.

As a laboratory marker

Creatine kinase is released from skeletal muscle into the blood during muscle injury or disease. It can therefore be used as a laboratory marker of skeletal muscle injury, for example due to rhabdomyolysis, myositis, muscular dystrophy. It can also be elevated after physical exercise.

The level of CK corresponds to the injury or disease. In case of Duchenne muscular dystrophy and rhabdomyolysis, the CK level can be 10 - 100x the upper reference limit.