Creatine kinase, or CK, is an enzyme found mainly in the brain, heart, skeletal muscles, and other tissues. CK, also called as phosphocreatine kinase or CPK, helps cells produce a biochemical reaction that results in high-energy molecules that cells use to perform normal functions. When creatine kinase combines with adenosine triphosphate (ATP) it produces phosphocreatine and adenosine triphosphate (ATP). The muscles use these energy molecules to contract muscle fibers. This reaction may also work in reverse, so that phosphocreatine and ADP may create ATP.
There are three types of creatine kinase, or isoenzymes, produced by the body. CK-MM is produced by skeletal muscle, CK-MB is produced by the heart, and CK-BB is produced by the brain. Under certain circumstances, CK-MM may leak from cells and enter the bloodstream. This happens when muscle is damaged, either by muscular injury, exercise, or as a result of a neuromuscular disorder.
Doctors may test for the presence of creatine kinase in the blood to help diagnose and evaluate disease in which muscular degeneration may occur. A blood sample of serum is obtained and levels of CK measured in units of enzyme per liter. Levels typically vary depending on gender, activity levels and other factors, but a normal range is 22 to 198 units per liter.
High levels of creatine kinase can indicate neuromuscular disease such as muscular dystrophy. Elevated CK may also indicate heart attack, acute kidney failure, polymyosotis, dermatomyositis, hypothyroidism, hypothermia, recent surgery, or a recent session of vigorous exercise. In the case of neuromuscular disease, high levels of CK can diagnose the disease before the appearance of other symptoms.
In cases of rhabdomyolosis, muscles break down very quickly, releasing cellular contents into the bloodstream. When this happens, creatine kinase levels may soar very high, indicating a dangerous condition where types of proteins called myoglobins can enter the kidneys. Renal failure may result. Rhabdomyolosis is not a condition in and of itself, but a symptom of other conditions in the body. It most commonly happens after severe injury or as the result of medication and requires immediate medical attention.
People who take statins to control cholesterol may need to have CK levels monitored regularly. A side effect of statins is muscle pain and weakness that can, in rare cases, lead to rhabdomyolosis and risk of kidney failure. Close monitoring of creatine kinase levels can alert the doctor to early signs of muscle breakdown so kidney damage may be prevented.