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Also known as creatine phosphokinase (CPK), creatine kinase (CK) is a cardiac enzyme that helps convert creatine to creatinine, a reaction that is necessary for metabolism and energy production. Creatine kinase is made up of three important isoenzymes:
- CK-BB (CK1). Exists primarily in the brain. CK-BB can be an important indicator of tissue damage in the brain from stroke, trauma or other causes.
- CK-MB (CK2). The primary indicator used to diagnose a heart attack because it exists in the highest amount in the heart. If CK-MB makes up more than 5 percent of a total CK level, a heart attack is suspected. CK-MB rarely rises following chest pain caused by angina, pulmonary embolism or heart failure, making it a valuable tool for determining whether a heart attack is the cause of chest pain. CK-MB levels typically increase to above normal levels about six hours after a person has had a heart attack. Furthermore, if one part of CK-MB (CK-MB2) is greater than another part (CK-MB1) by a ratio of 1.5 or more, then this is another indication that a heart attack has occurred. CK-MB levels can also be used after balloon angioplasty and other catheter-based techniques. Studies have shown an increased risk of sudden cardiac death with higher CK-MB levels after these procedures. CK-MB can also be found in small intestine, uterus, prostate, diaphragm, and tongue
- CK-MM (CK3). Exists primarily in skeletal muscle.
Creatine kinase tests may measure total CK levels or may break out the individual levels of CK-BB, CK-MB and CK-MM. Normal results are as follows:
- Total creatine kinase level (CK total). Normal levels are 25 to 130 micrograms per liter for men and 10 to 150 micrograms per liter for women. CK levels may be much higher in very muscular people, and infants up to 1 year may have levels up to four times the normal adult level. According to the American College of Cardiology (ACC), total CK levels should not be used in the diagnosis of heart attack. Instead, the College recommends that physicians rely on the more sensitive CK-MB levels, which are specific to the heart.
- CK-BB. Unless tissue damage in the brain has occurred, CK-BB levels will be undetectable.
- CK-MB. Normal range is from undetectable to 7 micrograms per liter.
- CK-MM. Normal range is from 5 to 70 micrograms per liter.
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