Creatine kinase (CK) is an enzyme found primarily in the brain, skeletal muscles, and heart. Conditions that cause damage to any of these three areas produce an elevated level of CK. For this reason, CK tests are often run to detect muscle damage, especially if someone is taking a drug such as a statin, using cocaine, or has been exposed to a toxin. If you’re experiencing chest pain or weakness your doctor may order a CK test to determine if you’ve had a heart attack. It is also common for doctors to use this test to evaluate the extent of sports injuries. Creatine kinase levels reflect the amount of muscle in the body, and as such men typically have higher levels than women. Finally, a CK test may be used to diagnose rhabdomyolysis, a condition characterized by the rapid breakdown of muscle tissue. It is worth noting that a normal level of CK does not necessarily mean that there is no muscle damage. It could mean that the damage occurred long enough ago for levels to return to normal. Frequently, a succession of CK tests are run as changes in CK levels due to muscle damage can take hours to present.
Normal CK levels change drastically depending on factors such as age, gender, and activity level. Generally, 24-204 U/L is considered normal.
A low CK level could be the result of alcoholic liver disease or rheumatoid arthritis. As CK levels are a reflection of total muscle mass, people who have been confined to bed rest for extended periods of time will display abnormally low CK levels. Women generally have lower CK levels than men, because they typically have less muscle mass. Additionally, a pregnant woman will display lower CK levels than a non-pregnant woman.
A high CK, or one that rises between samples, generally indicates recent muscle damage but will not reveal the location or cause. Chest pain and increased CK levels likely means that you’ve had a recent heart attack. Strenuous exercise will also cause CK levels to increase, and a level 100 times the normal range is a sign of rhabdomyolysis—the rapid breakdown of muscle tissue. This can be due to serious physical injury or it may point to a viral infection such as the flu, HIV, or herpes simplex virus. Seen in young boys, rhabdomyolysis may be a symptom of Duchenne muscular dystrophy.
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