Creatine Kinase (CK), also known as Creatine Phosphokinase or Phospho-creatine Kinase is an enzyme expressed by various tissues and cell types. Disruption of cell membranes due to hypoxia or other injury releases CK from the cellular cytosol into the systemic circulation. CK is a dimeric enzyme consisting of two subunits, which can be either B-(brain type) or M- (muscle type). These subunits associate to form three isoenzymic forms: CK-BB, CK-MM and CK-MB. These isoenzymes are expressed at different levels in various human tissues. Though CK-MM is the most abundant CK isoenzyme in the cardiac muscles, CK-MB constitutes about 20% of the total CK in the cardiac muscle tissue. Elevated levels of total CK is not specific to the myocardial tissue and may be observed in patients with skeletal muscle injury and certain other disorders but as CK-MB is more specific to myocardial tissue, CK–MB levels along with total CK can be considered as an important diagnostic indicator of myocardial infarction. The concentration of CKMB in the healthy adult is below 7.0ng/ml but it shows great increases in several malignant diseases, mostly primary coronary syndrome, myocardial injury and infarction. CK-MB has been found to be more sensitive and an early indicator of myocardial injury because it has a lower basal level and a much narrower normal range. Medical literature commonly reveals that following an acute myocardial infarction, CK-MB levels become elevated in 4 to 9 hours after the onset of chest pain, attain peak at 10 to 24 hours, and return to normal within 2 to 3 days. Use of CK-MB level as a percentage of total CK in the diagnosis of myocardial infraction is the most important clinical application of CK measurements in clinical chemistry.
Assessing to diagnose myocardial infarction in 12-48 hours